NEET Biology

NEET Biology Evolution Theory Of Evolution By Natural Selection

Recent study indicates that evolution refers to the alteration in the genetic makeup of a population resulting from the interplay of variations and natural selection.

• The notion of organic evolution was conceived by Darwin and Wallace.
• Aristotle posited that all living organisms can be systematically organized according to ascending complexity, with no gaps and no potential for positional alteration within the established hierarchy. The perspective on life is referred to as Scala Naturae.
• Evidence of evolution substantiates the occurrence of evolutionary processes. Notable proponents of organic evolution included Aristotle, Bacon, Kant, Buffon, and E. Darwin.
• The mutation hypothesis of evolution, proposed by de Vries, addresses certain limitations of Darwin’s theory.

NEET Biology Evolution Theories Of Evolution

The doctrines of organic evolution state that the world has evolved and not created as was believed earlier. Various theories have been put forward to explain organic evolution. Some of the important theories are as follows:

Read and Learn More NEET Biology Notes

1. Lamarck’s Theory of Inheritance of Acquired Characters (1744-1829): It is based on the following propositions.

1. Living organisms and their parts tend to increase in size continuously due to internal forces of life.
2. Production of a new organ in the body of organisms results from a new need for movement.
3. If an organ is used continuously and constantly, it tends to become highly developed, whereas its continuous disuse results in its disappearance.
4. Modifications produced or acquired during the lifetime of an individual are inherited.

• Lamarck’s Theory of Inheritance of Acquired Characters (1744-1829) Books written
  • Philosophic Zoologique
  • Organisation descerps vivont
  • Historic
  • Naturellecles Animax Sons Vertebrae.
• Lamarck’s Theory of Inheritance of Acquired Characters (1744-1829) Examples. Giraffes obtain their long necks by stretching them upwards to reach the available food in the form of leaves from tall trees. Eyes are reduced in moles because they live underground.
• Objections against Lamarckism. Lamarckism failed to meet the tests of observations. There is no evidence in support of the first proposition. The experiments conducted by Weismann in mice have discarded the law of inheritance of acquired characters.
• Neo-Lamarckism. A group of scientists Tower, Mendel, Morgan, Myar, and Smith have further studied Lamarckism and supported its modified form, which is known as Neo-Lamarckism.

2. Theory Of Catastrophism. Cuvier (1769-1832) is considered the father of modem palaeontology. Cuvier believed in the fixity of species. The occurrence of fossils of different rock strata was accounted on the basis of catastrophes. A succession of catastrophes have periodically destroyed all living things, followed each time by the successive creations of new and higher forms.

3. Theory Of Uniformitarianism. James Hutton (1878) and Charles Lyell (1932) established the concept of uniformitarianism which holds that slowly acting geological forces result in the formation of fossil-bearing rock strata.

4. Darwin’s Theory of Natural Selection ‘Descent of Man’ in 1871 – propounded by – Charles Darwin and Alfred Russel Wallace

Evolution Neet Notes

Summary Of The Theory Factors

Evolution Neet Notes

Objections To Darwinism

1. The type of variations that provide the raw material for natural selection are generally non-inheritable.
2. It does not explain the effect of use and disuse and the presence of vestigial organs.
3. Darwinism explains the survival of the fittest but not the arrival of the fittest. Darwin also put forward a hypothesis of pangenes in order to explain the possible mode of inheritance of these variations.
4. According to pangenesis theory each and every cell of the body produces minute primordia which are known as gemmules or pangenes. The gemmules from all parts of the body are carried by the bloodstream to the gonads where these accumulate in the germ cells.

5. Weismann’s Theory of Continuity of Germplasm. According to this theory, the cytoplasm of the animal body is differentiated into somatoplasm and germplasm. The germplasm produces gametes which transmit the characteristics of the parents to the offspring. The remaining body of the organism is formed of somatoplasm.

6. Recapitulation Theory of Haeckel. Haeckel (1811) proposed that “ontogeny repeats phytogeny ”, that is, the development of the individual repeats the evolutionary history of the race, condensing some stages and eliminating others.

7. Isolation Theory. The role of isolation in evolution was first emphasized by M. Wagner. He stated that any factor or mechanism which separates the individuals of a species into groups, so that these are unable to intermingle and interbreed, constitutes the isolating mechanism and is helpful in the progress of evolution.

8. DeVries’ Theory of Mutation. De Vries suggested that variations which are important for evolution are sudden and large; which he called mutations or saltation

Evolution Neet Notes

Salient Features Of The Mutation Theory: On the basis of his observations, Hugo de Vries (1901) put forward a theory of evolution, called mutation theory. The theory states that evolution is a jerky process where new varieties and species are formed by mutations (discontinuous variations) that function as the raw material of evolution. The salient features of mutation theory are

1. Mutations or discontinuous variations are the raw material of evolution.
2. Mutations appear all of a sudden. They become operational immediately.
3. Unlike Darwin’s continuous variations or fluctuations, mutations do not revolve around the mean or normal character of the species.
4. The same type of mutations can appear in a number of individuals of a species.
5. All mutations are inheritable.
6. Mutations appear in all conceivable directions.
7. Useful mutations are selected by nature. Lethal mutations are eliminated. However, useless and less harmful ones can persist in the progeny.
8. Accumulation of variations produces new species. Sometimes a new species is produced from a single mutation.
9. Evolution is a jerky and discontinuous process.

Evolution Neet Notes

Modern Synthetic Theory has evolved dm in; the last century through an accumulation of fuels and theoretical conclusions from a number of scientists, Dobzhansky (1937) emphasized the role of genetic changes in populations in the process of evolution. Julian Huxley and Ernst Mayr have explained the mechanism of origin of variations in higher animals,

1. Genetic Variations in n Population: Population is the unit of Involution
   • Mechanism Of Genetic Change
     • Gene mutation
     • Chromosomal aberrations
     • Recombination of genes
     • Hybridization
2. Natural Selection: It really means differential reproduction i.c. some members of a population reproduce at a higher rate and leave more surviving offspring in the next generation than others. The organisms that produce more offspring contribute a proportionately greater percentage of genes to the gene pool of the next generation.
   • What really matters in evolution is not how well or poorly the individuals can face the environment, but how many of their young ones survive to become parents of the next generation.
3. Speciation: Species are the group of actually or potentially interbreeding natural populations that are reproductive and isolated from other such groups. The formation of new species may be caused by the gradual drifting away of two or more populations of a single species until such time they cease to interbreed.

NEET Biology Evolution Factors Causing Genetic Divergence In The Populations

1. Mutations. These are the changes in the chemical constitution of the DNA in the chromosomes of an organism. Depending upon the mutation, selection will operate either for or against the mutated gene.
2. Recombination. Brings about new combinations of old genes present in the gene pool of a population as a result of interbreeding, crossing over at the time of meiosis, free assortment of genes at the time of gamete formation etc.
3. Genetic Drift Or Random Drift. In small populations, frequencies of particular alleles may change drastically by chance alone. Such changes in allele frequencies occur randomly, as if the frequencies were drifting, and are thus known as genetic drift. For this reason, a population must be large to be in Hardy-Weinberg equilibrium.
   • If the gametes of only a few individuals form the next generation, the alleles may by chance not be representative of die parent population from which they were drawn, for example when a small number of individuals are removed from a bottle containing many.
   • By chance, most of the individuals removed are blue, so the new population has a much higher population of blue individuals than the parent one had.

Mechanism Of Origin Of Species. There are two distinct ways in which new species arise from the pre-existing ones.

1. Speciation. Splitting of species into two or more species.
2. Transformation In Time. Transformation of the old species into new ones in due course of time.

• Geographical Speciation. The geographic isolation of a population of pre-existing species into sub-populations for a sufficiently long time produces genetic changes thus changing them into new species.
• Sympatric Speciation. It generally takes place due to a sudden new effective mutation occurring in a single individual.
• Role Of Hybridization And Polyploidy In Speciation: Generally the members of different species do not interbreed and produce fertile offspring. But sometimes, the individuals of two different but closely related species may interbreed to produce fertile young ones. This phenomenon is called hybridization.

Rapid Speciation Occurs By Polyploidy: Hybridization between even closely related species is prevented by a number of barriers. Examples. Polyploidy is uncommon in animals but about one-third of the plant species are polyploids example,

1. In wheat (2N=14), there are species with chromosome numbers 14, 28 and 42
2. In rose, there are species with 14, 28, 42 and 56 chromosomes.
3. Experimental formation of Raphanobrassica (Chromosome number = 36) by crossing radish (Raplianus, 2N=18) and cabbage (Brassica, 2N=18).

Isolation: It is the segregation of the population of a species into smaller units of individuals by certain mechanisms so as to prevent interbreeding among them.

Isolating Mechanism is the process of producing and maintaining reproductive isolation in a population. This can be brought about by mechanisms acting before or after fertilization.

Theodosius Dobzhansky suggested a classification of isolating mechanism

Theodosius Dobzhansky External Barriers: The premating mechanism prevents interspecific mating: Potential mates do not meet due to

1. Geographical isolation
2. Climatic isolation
3. Seasonal isolation
4. Habitat isolation
5. Isolation due to distance.
   • Potential mates meet but do not mate, it is ethological isolation
     • Copulation attempted by transfer of mates does not take place due to
     • Mechanical isolation
     • Physiological isolation

Theodosius Dobzhansky Internal Barriers: Post-mating mechanism. Reduce full success of interspecific isolation

1. Gametic Mortality. Sperms are transferred but eggs are not fertilized
2. Zygote. Eggs are fertilised but the zygote is inviable
3. Hybrid Inviability. Zygote produces F, a hybrid of reduced viability
4. Hybrid Sterility. Hybrid is produced but partially or completely sterile

Evolution NEET Important Questions

Kinds Of Isolation. They are given below:

1. Geographical Isolation. The various physical barriers, such as mountain ranges, rivers, deserts, water connections, etc; play an important role in the isolation of a population into units.
2. Isolation Due To Sheer Distance Apart. The members of a widely distributed species, which occupy a large extent of territory without natural barriers, may become isolated since they are unable to cover great distances. Thus the members of one part interbreed among themselves and do not reach other parts.
3. Climatic Isolation. The abrupt climatic differences in the range of distribution of species cause its separation into sub-units. The climatic factors may be temperature, moisture, mineral concentration and chemical composition of the surroundings.
4. Mechanical Isolation. Animals of different species are unable to interbreed due to the differences in size and structure.
5. Ecological Isolation. Due to different ecological habits, the organisms become isolated and interbreeding between them is prevented.
6. Physiological Isolation. Certain species are established only on the basis of some physiological differences developed between them. For example, in certain species of Drosophila mating is not possible among the members of different species. In Drosophila, the vaginal mucous membrane swells up after mating. This swelling lasts for a few hours if the mating is among the members of the same species, but continues for days if the mating is interspecific. This precludes the passage and eggs fail to come out.
7. Reproductive Isolation. In some species closely allied species are intersterile due to the differences in their copulatory organs. For example, in insects, the copulatory organs are developed on lock and key arrangement i.e., only one type of key fits into one definite pattern of lock.
8. Gametic Isolation. Interbreeding is prevented by gametic inviability. The sperms of one species are either unable to survive or poorly survive in the genital tract of the females of other species.
9. Hybrid Inviability. In other cases even if the gametes survive and bring about fertilization, the zygote is either unable to develop further or the embryo dies after developing for some time.
10. Hybrid Sterility. In some cases, the hybrid formed by the mating between different species is viable but is either sterile or produces fewer offspring, for example, Mules.
11. Changes In The Developmental Rhythm. Speed of development and length of life-cycle changes split up the species into groups and genera into species.
12. Psychic Isolation. Animals have a tendency to mate with like forms. They fail to copulate because of differences in mating behaviour and nest-building habits.

NEET Biology Evolution Neo Darwinism

Neo-Darwinism gains strength from a number of evidence like industrial melanism, the origin of DDT-resistant mosquitoes, geographical distribution of sickle cell anaemia etc.

Five Major Causes Of Evolutionary Changes Accepted By Neo-Darwinism

1. Gene mutation
2. Chromosomal mutations
3. Genetic recombination
4. Natural Selection
5. Reproductive isolation

G.L. Stebbins (1966—76) gave this theory in the present form as follows: Five factors have been identified as main bases

There are also accessory factors like gene migration and hybridization to increase genetic variability. Lastly, the chance factors (genetic drift) in a small population are also relevant in the evolution of the new species.

Evolution NEET Important Questions

Neo Darwinism Examples

1. Industrial Melanism. Before the industrial revolution, the dull grey forms of peppered moth – Bistort betuJaria were dominant; the carbonara form (black) was rare because it was susceptible to predation by birds. The reason was that it was conspicuously visible while resting on tree trunks.
   • The Industrial Revolution resulted in large-scale smoke which got deposited on tree trunks turning them black. Now grey varieties became susceptible and the black forms flourished.
   • Replacement of coal by oil and electricity, reduced soot production – the frequency of grey moths increased again.
2. Drug Resistance. The drugs which eliminate pathogens become ineffective in the course of time because those individuals of pathogenic species can tolerate them, survive, and flourish to produce tolerant populations.
3. Sickle Cell Anaemia And Malaria. Individuals homozygous for sickle cell anaemia die at an early age. In heterozygous individuals, the cells containing abnormal haemoglobin become sickle- shaped. In fact, when RBC becomes sickle-shaped, it kills malarial parasites effectively so that these individuals are able to cope with malaria infection much better than normal people.
4. Favism, Glucose 6 phosphate dehydrogenase deficiency is a common abnormality in Negroids. Haemoglobin gets denatured and is deposited on the cell membrane. If such persons eat beans, haemoglobin is destroyed.

J. Lederberg And E. Lederberg provided experimental evidence for ‘selection* in bacteria. By using the replica plating technique, they demonstrated the processes of ‘selection* of antibiotic-resistant strains of bacteria.

Genetic Basis Of Adaptation: Lederberg’s Replica Plating Experiment is a good example of the genetic basis of adaptation.

1. After introducing penicillin, in the culture plate, it was found that some colonies were resistant to it. Bacteria acquired this ability due to mutations (preadaptive) which occurred before exposure to penicillin.
2. The new environment only selects such mutations.
3. Lamarckian explanation of this could be that the penicillin induced changes in some bacteria enabling them to grow in this medium. Thus these bacteria became adapted to live in a penicillin medium.
4. The Darwinian interpretation could be that the colonies had two types of strains: Penicillin-sensitive and penicillin-resistant arising by mutation. Before the use of penicillin, the suitable condition was for sensitive strain, hence after using penicillin they were wiped out, but was favourable for resistant strain. Thus natural selection operates here as advantageous to the resistant strain.

Evolution NEET Important Questions

Gene Frequency. Suppose two alleles A and A of a gene exist in a population. Suppose X individuals have genotype AA. Y have Aa, Z have aa. N (Total no. of individuals) = X + Y+ Z.

The no. of alleles would be 2 x N.

The ratio of A alleles (p) in population = \(\frac{2 X + Y}{2N}\) = \(\frac{X + 0.5 Y}{N}\)

This is called the gene frequency of A. Gene frequency of ‘a’ would be q = \(\frac{Y + 2 Z}{2N}\) = \(\frac{0.5 Y + Z}{N}\)

Selection Change. Over a period of time, the criteria of natural selection also change. As a result, the genetic composition and the direction of evolution also change.

NEET Biology Evolution The Hardy Weinberg Equation

Hardy-Weinberg Equation developed independently by G.H. Hardy, an English mathematician, and G. Weinberg, a German physician, in 1908, describes the relationship between allelic frequencies and genotypic frequencies in successive generations of a population that is at equilibrium is not evolving.

The Hardy-Winberg equation is p² + 2pq + q² = 1

where p = frequency of one allele (for example, A) at a locus

q = frequency of the alternative allele (for example, a) at the same locus

p² = frequency of the genotype homozygous for the allele present in frequency p (for example, A/A)

2pq = frequency of the heterozygous genotype (for example, A/a)

q² = frequency of the genotype homozygous for the allele present in frequency q (for example, a/a)

• If the frequency of one of the alleles (for example, p) is known, then the frequency of the other allele (q = 1 -p) can be known and the frequencies of the homozygous genotypes (p and q²) as well as those ofthe heterozygous genotype (2pq) can be calculated.
• Or, if the frequency of homozygous recessive individuals in the population (a/a, or q²) is known, then the frequencies of the allele (q) and the A allele (p or 1 – q) can be calculated.
• It is then possible to predict genotypic frequencies in the present and future generations. The Hardy-Weinberg principle states that the frequencies of alleles and genotypes remain the same from generation to generation- are not altered by genetic recombinations-provided that the following conditions hold.

1. No mutations
2. An infinitely large population (no genetic drift)
3. No emigration out of or immigration into the population (no gene flow)
4. Random matings between individuals (no assortative matings)
5. Equal reproductive success among the genotypes (no natural selection)

Illustration: An investigator has determined by inspection that 16% of the human population has a recessive trait. Using this information, we can complete all the genotype and allele frequencies for the population, provided the conditions for Hardy-Weinberg equilibrium are met.

Given: q² = 16% = 0.16 are homozygous recessive individuals.

Therefore, q = √0.16 = 0.4 = frequency of recessive allele

p = 1.0 – 0.4 = 0.6 = frequency of dominant allele

p² = (0.6)(0.6 = 0.36 = 36% are homozygous dominant individuals) 84% have the dominant phenotype

2 pq = 2(0.6)(0.4) = 0.48 = 48% are heterozygous individuals = 1.00-0.52 = 0.48

Present-Day Concept Of Evolution: A modified form of Darwin’s theory, lienee is often called Neo-Darwinism.

Also called the synthetic theory of evolution (synthesis of Darwin’s and Hugo de Vries’ theories). According to this theory, only genetic variations are inherited. It includes the following factors.

1. Genetic Variations in a population occur by mutations, genetic drift (elimination of gene of certain traits due to migration or death of a section of a population), geneflow (addition or removal of alleles when individuals enter or leave a population), gene recombination, hybridization, etc.
2. Heredity, i.e., the transmission of characters from parents to offspring plays an important role in the mechanism of evolution.
3. Natural Selection selects those members which have traits that enable them to grow up and reproduce at a faster rate. It is of four types:
   • Stabilizing Selection: Keeps population genetically constant and favours normal phenotypes whereas eliminates extreme variants.
   • Directional Selection: Produces a regular change within a population in one direction and favours non-average phenotypes.
   • Disruptive Selection: Favours extreme or more adaptable phenotypes hence poplution is disrupted into two groups.
   • Cyclic Selection: Maintains genetic differences in a population and fixes all the alleles of a gene pool.
4. Speciation occurs which is die formation of new species from existing ones by evolutionary means. It is of four types:
   • Multiplicative: Splitting of a species into new species which may be gradual (occurring in many generations) or instant (occurring in a single generation).
   • Phyletic: Replacement of one species by another without an increase in number.
   • Speciation By Fusion: Here two species merge into one.
   • Quantum: Speciation by reproductive isolation due to chromosomal rearrangements.
5. Reproductive Isolation i.e., prevention of interbreeding between populations of two different species is accomplished by either premating methods that may be mechanical, ethological, seasonal and gametic isolation or post-mating methods like incompatibility, hybrid sterility, etc. (post-mating).

• Mutations. A mutation is a random inheritable change in the genetic material. It may be due to changes in the structure of chromosomes, number of chromosomes, and gene mutation (Change in sequence of nucleotides).
  • Mutation is a recurrent event because a given length can undergo only a limited number of chemical changes if given enough time, each of these will appear again and again. Thus, in a hypothetical population in which all individuals are homozygous AA, the allele A will be eventually introduced by mutation.
• Mutations Are Regarded As Fountainheads Of Evolution. Recombination. During meiosis, crossing over causes reshuffling of gene combinations which provides new combinations of existing genes and alleles.
  • This is the essence of recombination. It may bring together the alleles that arose at different times and places. Recombination can occur not only between genes but also within genes resulting in the formation of a new allele. As it adds new alleles and a combination of alleles to the gene pool it is an agent of evolution.
• Gene Migration. Because few populations are completely isolated from other populations of the same species, usually some migration between populations takes place.
  • Therefore, members of a population may enter a  new population due to migration.
  • If the migrating individuals breed within the new population, the immigrants will add new alleles to the local gene pool of the host population. This is called gene migration.
• Genetic Drift (Or Wright’s Effect). Random change occurring in the allele frequency by chance alone is called genetic drift.
  • It is the change in the number and frequency of genes (alleles) that occurs by chance – and plays an important role in evolution.
  • It operates in small isolated populations by persistent in-breeding. As a result, some alleles become permanently fixed. While some alleles undergo change in their frequency and some others disappear completely.
  • When a species is split into many isolated populations without migration or mixing, its genetic composition is mainly determined by genetic drift.
  • In the case of Biston betulciria even though the grey moth was easily visible it was not that dark to escape predation.
  • Rather sometimes in areas with a high population of grey moths, birds used to prey on more black moths due to sheer chance.
• Founder Effect. When a population gets separated from the existing population it becomes the founder of a new population. This is called the founder effect which is the result of genetic drift i.e., by chance.
• Genetic Bottleneck. Wien in a season the one population leaves a few individuals of the population which become the founder of the new population then it will produce only a few genes by selection i.e. by chance new population emerges and it is similar to a bottle in which only certain population is allowed to flow as in the neck of the bottle.
• Gene Flow: Gene flow is the movement of alleles from one population to another. It can be a powerful agent of change because members of different populations may exchange genetic material. Sometimes gene flow is obvious, as when an animal moves from one place to another.
  • If the characteristics of the newly arrived animal differ from those of the animals already dire, and if the newcomer is adapted well enough to the new area to survive and mate successfully, the genetic composition of the receiving population may be altered.
  • Other important kinds of gene flow are not as obvious. These subtler movements include the drifting of gametes or immature stages of plants or marine animals from one place to another.
• Male Gametes of flowering plants are often earned great distance by insects and other animals that visit their flowers.
• Seeds may also blow in the wind or be carried by animals or other agents to new populations far from their place of origin.
• Gene flow may also result from the mating of individuals belonging to adjacent populations.
• Gene flow can alter the genetic characteristics of populations and prevent them from maintaining Hardy- Weinberg equilibrium.

Evolution NEET Revision Notes

Kinds Of Selections

1. Stabilising selection
2. Directional selection
3. Disruptive selection

Even low levels of gene flow tend to homogenize allelic frequencies among populations and thus keep the populations from diverging genetically.

• In some situations, gene flow can counter the effect of natural selection by bringing an allele into a population at a rate greater than that at which the allele is removed by selection.
• Migration is the movement of individuals from one population to another population.
• Emigration is the migration of individuals out of an area.
• Immigration is the migration of individuals into an area. AHopatric speciation. The speciation by the geographical separation of two populations and the divergence of the population.
• Sympatric Speciation. When a sub-population becomes reproductively isolated in the midst of its parent population this is called sympatric speciation.
• Balancing Selection. A heterozygous condition in sickle cell anaemia (H^A/H^S) survived the malarial condition and balanced the loss by sickle cell anaemia is called balancing selection.
• Biological Species concept. A sexually interbreeding population which is separated from other species by reproductive isolations.
• Evolutionary Species Concepts. An evolutionary species is a lineage evolving separately from others with its own unitary evolutionary role and tendencies.
• Convergent Evolution (Adaptive Convergence). The development of similar adaptive functional structures in unrelated groups of organisms is called convergent evolution. Example: Wings of insect, bird and bat.
  • Thus analogous organs show convergent evolution (adaptive convergence). When adaptive convergence is found in closely related species. It is called “Parallel Evolution” Example: development of running habit in deer (2-toed) and horse (1-toed with two vestigial splint bones.)
• Stabilizing Selection
  1. Stabilizing selection operates in a constant or unchanging environment.
  2. Stabilizing selection introduces homogeneity in the populations.
  3. Stabilizing selection favours average or normal individuals and eliminates over-specialised as well as less-specialized or less adapted individuals.
  4. Stabilizing selection checks the accumulation of mutations that may lower the fitness of species in unchanging environments.
  5. Stabilizing selection tends to arrest variance and evolutionary change.
  6. Stabilizing selection operates rarely because the environment is rarely constant.
     • Stabilizing Selection Examples
       1. Stabilizing selection in sparrows observed by H.C. Bumpus in 1S99.
       2. Stabilizing selection in Land Snails was observed by W.F.R. Weldon in 1901.
       3. Mortality of babies
       4. Stabilizing selection in red checkered moths (Panaxiadominula) observed by E.B. Ford.

Evolution NEET Revision Notes

Directional Selection:

This selection process functions in reaction to incremental alterations in environmental variables.

• It functions within the spectrum of phenotypes present in the population and applies selection pressure that shifts the mean phenotype towards a phenotypic extreme.
• When the mean phenotype aligns with the new optimal environmental conditions, stabilizing selection will prevail.
• This type of selection induces evolutionary change by creating a selection pressure that promotes the proliferation of novel alleles within the population.
• Directional selection underpins artificial selection, whereby the selective breeding of phenotypes exhibiting desirable qualities enhances the prevalence of those phenotypes in the population.
• D.S. Falconer conducted a series of tests in which he picked the heaviest mice from a population at six weeks of age and allowed them to inbreed. He also chose the lightest mice and permitted them to inbreed.
• This selective breeding based on mass led to the emergence of two populations: one exhibiting an increase in bulk and the other a decrease
• Following the cessation of selective breeding, neither group reverted to the original population mass of around 22g. This indicated that the artificial selection of phenotypic traits resulted in certain genotypic selection and a reduction of alleles within each population.

Disruptive Selection. Fluctuating conditions within the environment may favour the presence of more than one phenotype in a population. It was studied in sunflowers.

NEET Biology Evolution Theory Of Evolution By Natural Selection Synopsis

The unit of evolution is the population. The unit of natural selection is individual (phenotype).

• An Isolating Mechanism is a means of producing and maintaining reproductive isolation within a population. This can be brought about by mechanisms acting before or after fertilisation. Theodosius Dobzhanskv suggested a classification of isolating mechanisms.
• Adaptive Radiations. Evolution of groups of animals in different directions.
• Of all the species that have ever lived more than 99% have gone extinct
• Danvin used the breeding of domestic animals, known as artificial selection as evidence of evolution. In artificial selection, humans are the selective agents, while in natural selection, the environment is the selective agent.
• Darwinism Fitness. In an individual it is a measure of its ability, relative to others in the population, to pass genes to the next generation.
• The branch of Biology that emerged from the synthesis of Darwinian Evolution and Mendelian genetics is called Population Genetics
• Parallelism is the adaptive convergence of closely related species in evolution.
• Genetic variation that parallels a gradient (for example, Rainfall) is called Cline.

Darwin regarded continuous variations to be more important since discontinuous variations being mostly harmful would not be selected again.

1. G6PD is an X-chromosome-linked trait. Clinical features
2. Drug-induced hemolytic anaemia, for example, sulphonamide, primaquine nitro furantin and phenacetin. Ingestion of the drug is followed by fever, malaise, prostration and passage of dark urine
3. Favism
4. Neo-natal jaundice Diagnosis is established by enzyme assay.

Evolution MCQs For NEET Biology With Answers

Question 1. Which one is the common point in Lamarckism and Darwinism?

1. Origin of the idea of organic evolution
2. Continuity of germplasm.
3. Mutation
4. The idea of evolution.

Answer: 4. The idea of evolution.

Question 2. Genetic drift is on account of:

1. Variation
2. Mutation
3. Increase in population
4. No change in population.

Answer: 3. Increase in population

Question 3. Reproductive isolation between segments of a single population is termed:

1. Allopatry
2. Population divergence
3. Sympatry
4. Disruptive isolation.

Answer: 3. Sympatry

Evolution – NEET Questions Question 4. The present Giraffe has a long neck as compared to its ancestors. According to the present-day view could be due to the:

1. Natural selection
2. Isolation
3. Speciation
4. Inheritance of acquired characters.

Answer: 1. Natural selection

Question 5. The appearance of ancestral characters in the new bombs, such as the tail, multiple mammae etc. is known as:

1. Homologous
2. Analogous
3. Atavism
4. Vestigial.

Answer: 3. Atavism

Question 6. Nowadays Lamarckian theory is being reviewed in the light of the modern concept of evolution under the heading Neo-Lamarckism. Who proved that the genes are influenced by physical and chemical factors so that they bring remarkable changes to the offspring

1. Tower
2. Harrison
3. Hoffman
4. Both 1 and 2.

Answer: 4. Both 1 and 2.

Question 7. According to the Neo-Lamarckism:

1. Acquired characters influence the somatic cells
2. Acquired characters influence the chromosomes or genes
3. Somatic characters are not inherited while characters of gametes are inherited by the offspring
4. All the above three.

Answer: 2. Acquired characters influence the chromosomes or genes

Question 8. One of the following is most essential of evolution:

1. Mutation
2. Hereditary characters
3. Adaptations
4. Nature.

Answer: 1. Mutation

Evolution – NEET Questions Question 9. Changes in genetic characters on accumulation, leading to the formation of new individuals is characteristics of:

1. Non-directional
2. Genetic drift
3. Divergent evolution
4. Macroevolution.

Answer: 3. Divergent evolution

Question 10. Radiations with successful adaptations in the case of insects over a major period are a result of the:

1. Microevolution
2. Genetic divergence
3. Mega evolutions
4. Macroevolution.

Answer: 4. Macroevolution.

Read and Learn More NEET Biology Multiple Choice Question and Answers

Question 11. The term used for similarity in organ structure seen in great diversity is:

1. Homology
2. Analogy
3. Symmetrical
4. Identical.

Answer: 1. Homology

Question 12. Darwinism fails to explain:

1. Usefulness of all organs
2. Retrogression
3. Progression
4. Presence of vestigial organs.

Answer: 4. Presence of vestigial organs.

Question 13. Fishes to mammals have a similar structure with respect to:

1. Forebrain alone
2. Midbrain alone
3. Hindbrain alone
4. All three regions.

Answer: 4. All three regions.

Question 14. Balancing selection promotes:

1. Homozygotes
2. Heterozygotes
3. Polyploids
4. Recessive traits alone.

Answer: 2. Heterozygotes

Evolution MCQ for NEET Question 15. Cladogenesis refers to:

1. Convergence of different genetic lines
2. Divergence of genetic lines from a common ancestor
3. Independent evolution
4. Formation of new species.

Answer: 2. Divergence of genetic lines from a common ancestor

Question 16. Allopatric speciation is due to:

1. Mutation
2. Geographical separation of population
3. Migration of members of a species from one to another population
4. Hybridization between closely related species.

Answer: 2. Geographical separation of population

Question 17. The most complex cellular structures are found in:

1. Bacteria
2. Algae
3. Protozoa
4. Fungi.

Answer: 3. Protozoa

Question 18. The oldest fossil of a mammal is from the:

1. Permian period
2. Jurassic period
3. Triassic period
4. Cretaceous period.

Answer: 3. Triassic period

Question 19. Successful adaptation simply means:

1. An increase in fitness
2. Moving to a new place
3. Producing viable offsprings
4. Evolving new characteristics.

Answer: 3. Producing viable offspring

Question 20. The unit of evolution is now known to be the:

1. Individual
2. Family
3. Population
4. Species.

Answer: 3. Population

Evolution MCQ for NEET  Question 21. The unit of natural selection is the:

1. Individual
2. Family
3. Population
4. Species.

Answer: 1. Individual

Question 22. The total collection of genes at any one time in a unit of evolution is called the:

1. Genotype
2. Gene pool
3. Multiple allelic groups
4. Demotype.

Answer: 2. Gene pool

Question 23. A change in the relative abundance of an allele (the allelic frequency) within a population, over a succession of generations is called:

1. Micro-evolution or adaptive evolution
2. Macro-evolution or speciation
3. Co-evolution
4. Phylogenetic evolution.

Answer: 1. Micro-evolution or adaptive evolution

Question 24. Micro-evolution can be measured by comparing observed allelic frequencies with those predicted by:

1. Chance
2. Hardy Weinberg equation
3. Mendelian ratios
4. All known environmental factors.

Answer: 2. Hardy Weinberg equation

Question 25. A potential danger to a population that has been greatly reduced in number is the following:

1. Loss of genetic viability
2. The tendency towards assortative mating
3. Reduced gene flow
4. Hardy Weinberg disequilibrium.

Answer: 1. Loss of genetic viability

Question 26. All alleles originate from:

1. Mutations
2. Cross-overs
3. Gene flow
4. Non-disjunctions.

Answer: 1. Mutations

NEET MCQ Questions With Answers Question 27. A beneficial allele increases more rapidly in frequency if it is:

1. Recently mutated
2. Rare
3. Dominant
4. Recessive.

Answer: 3. Dominant

Question 28. Sympatric speciation occurs most commonly in:

1. Mammals
2. Fishes
3. Amphibians
4. Birds.

Answer: 2. Fishes

Question 29. Reproductive isolation in sympatric speciation develops without a:

1. Change in chromosome number
2. Barrier to mating
3. Geographical barrier
4. The barrier to gene flow.

Answer: 3. Geographical barrier

Question 30. Darwin found that South American fossils are most similar to:

1. Australian fossils
2. Asian fossils
3. Living species of South America
4. Living species of North America.

Answer: 3. Living species of South America

Question 31. Darwin believed that a Giraffe has a long neck because:

1. A creator designed it that way
2. Catastrophes eliminated short-necked form
3. Its ancestors stretched their necks to get food
4. Ancestral Giraffes with slightly longer necks than others got more food and left more surviving offspring.

Answer: 4. Ancestral Giraffes with slightly longer necks than others got more food and left more surviving offspring.

NEET MCQ Questions With Answers Question 32. According to Darwin, two different areas within a continent have different species because they have different:

1. Evolutionary mechanism
2. Ancestors
3. Environments
4. Evolutionary times.

Answer: 3. Environments

Question 33. The population of Bi’s ton betularia changed from 1% dark 99% light individuals, 99% dark and 1% light individuals between 1848 to 1898. The selective agent causing the change was:

1. Humans
2. Toxins from smoke
3. Birds
4. Tree bark.

Answer: 3. Birds

Question 34. The most important evidence since Darwin bears on his theory has been the area of:

1. Palaeontology
2. Genetics
3. Comparative anatomy
4. Comparative embryology.

Answer: 2. Genetics

Question 35. Phylogeny describes a species:

1. Morphological similarities with other species
2. Reproductive compatibilities to other species
3. Evolutionary history
4. Geographical distribution.

Answer: 3. Evolutionary history

NEET Biology Evolution MCQs Question 36. Plants and animals of the Galapagos Islands resemble most closely the plants and animals of:

1. North America
2. South America
3. Asia
4. Australia.

Answer: 2. South America

Question 37. Similar traits resulting from similar selection pressures acting on similar gene pools are:

1. Coevolution
2. Convergent evolution
3. Divergent evolution
4. Parallel evolution.

Answer: 4. Parallel evolution.

Question 38. The process of evolution:

1. Is a continuous process
2. Is a discontinuous process
3. Was continuous in the beginning but discontinuous now
4. Was discontinuous.

Answer: 1. Is a continuous process

Question 39. Organic evolution means:

1. Life began in the sea
2. Fossils are old
3. Descent with modifications
4. Man descended from monkeys.

Answer: 3. Descent with modifications

Question 40. Evolution is generally:

1. Progressive
2. Retrogressive
3. Standstill
4. None of the above.

Answer: 1. Progressive

Question 41. Evolution means:

1. History of race
2. Development of race
3. History and development of race with variations
4. Progressive development of the race.

Answer: 3. History and development of race with variations

NEET Biology Evolution MCQs Question 42. Charles Darwin toured in a ship for 5 years. It was:

1. Vikrant
2. Alexander
3. Phillips
4. Beagle.

Answer: 4. Beagle.

Question 43. The modern theory of organic evolution is based on:

1. Genetic variation
2. Natural selection
3. Isolation
4. All the above three.

Answer: 4. All the above three.

Question 44. Genetic variation arises by:

1. Recombination (crossing over)
2. Chromosomal aberrations
3. Mutation
4. All the above.

Answer: 4. All the above.

Question 45. Genes mutate by:

1. Substitution of a base
2. Addition of a base
3. Deletion of a base
4. All the above.

Answer: 4. All the above.

Question 46. The natural selection really means:

1. Struggle for existence
2. Differential reproduction
3. Survival of the fittest
4. Elimination of the unfit.

Answer: 2. Differential reproduction

Question 47. Salutations is the name given to:

1. Lethal variations
2. Blastogcnic variations
3. Continuous variations
4. Discontinuous variations.

Answer: 4. Discontinuous variations.

Question 48. The role of isolation in evolution is:

1. Creation of new species
2. Maintenance of an existing species
3. Evolutionary divergence
4. Extermination of a species.

Answer: 1. Creation of new species

Question 49. Which is the most important factor for the development of a new species?

1. Extensive inbreeding
2. Extensive outbreeding
3. Geographical isolation
4. None of the above.

Answer: 2. Extensive outbreeding

Question 50. There is more competition for survival between:

1. Different animals of the same niche
2. Some animals of the same niche
3. Different animals of different niche
4. Same animals of different niches.

Answer: 2. Same animals of the same niche

Question 51. Speciation depends on the sum total of adaptive changes preserved by:

1. Natural selection
2. Human conservation
3. Isolation
4. Environment.

Answer: 3. Isolation

Question 52. Separation of a variant population from the original population by a mountain is called:

1. Geographical isolation
2. Ecological isolation
3. Economical isolation
4. Temporal isolation.

Answer: 1. Geographical isolation

Question 53. The propounder of the theory of Natural Selection was:

1. Mendel
2. Darwin
3. De Vries
4. Lamarck.

Answer: 2. Darwin

Question 54. The doctrine of evolution is particularly concerned with:

1. Gradual changes
2. Environmental condition
3. Theory of special creation
4. Spontaneous growth.

Answer: 1. Gradual changes

Question 55. The theory of inheritance of acquired characters was proposed by:

1. Mendel
2. Darwin
3. Lamarck
4. De Vries.

Answer: 3. Lamarck

NEET Biology Evolution MCQs Question 56. Darwin was influenced by one of the following in proposing the theory of his natural selection:

1. Cell theory
2. Mendel’s Laws of Inheritance
3. Overflow of population
4. Malthus’s theory of population.

Answer: 4. Malthus’s theory of population.

Question 57. Organic evolution refers to:

1. Evolution of organs
2. Orderly changes based on plans of the past
3. Drastic changes with no resemblance to the past
4. Orderly changes over long periods.

Answer: 2. Orderly changes based on plans of the past

Question 58. Retrogressive evolution refers to:

1. Elimination of structural diversity
2. Elimination of behavioural traits
3. Reduction in structure of complex but primitive organisms
4. Degeneration of advanced organisms.

Answer: 3. Reduction in structure of complex but primitive organisms

Question 59. The various concepts such as conflict, struggle and survival were first introduced by:

1. Darwin
2. Heraclitus
3. Empedocles
4. Anaximander.

Answer: 1. Darwin

Question 60. De Vries worked on the plant:

1. Pisum
2. Lathyrus
3. Oenothera
4. Mirabilis.

Answer: 3. Oenothera

NEET Biology Evidence Of Evolution Relationship Among Organisms

Organic evolution is also stated as ‘Descent with modification’ (Darwin, 1859)

Empedocles (493—435 B.C.). Founder of the concept of Evolution.

Herbert Spencer (1820-1903). Coined the term evolution.

Biological evolution has given rise to a large number of different kinds of organisms.

NEET Biology Evidence Of Evolution Evidence In Support Of Evolution

The types of evidence which support organic evolution are, morphological, anatomical, embryological, palaeontological, biogeographical, physiological, and biochemical.

Read and Learn More NEET Biology Notes

NEET Biology Evidence Of Evolution From Taxonomy

Classification of animals both present and extinct is based upon their natural similarities and dissimilarities which establish their genealogical relationship and common ancestry.

Palaeobiological study helps in understanding and locating hydrocarbon sources.

Evidence Of Evolution NEET Notes

Palynofossils—the tiny microscopic spores, pollen, and other vegetal remains of the past—assist us in interpreting ancient environmental conditions favourable for organic matter accumulation and its conversion to fossil fuels by transformation and subsequent thermal alteration.

Genclogieal lice was first drawn by Lamarck (1809).

• The levels of classification are Phylum → Class → Order → Family → Genus → Species.
• All similar species are grouped together in one genus, all such genera in one family and so on.

Evolution Of Plants

• Diverse life processes, including energy transformation, macromolecule synthesis, genetic coding, and various biochemical reactions, exhibit similarities among diverse creatures.
• The parallels in biological processes reinforce the notion that every living being originated from a shared primordial ancestor and emerged through evolution.
• Evolutionary change is an essential trait of all living species.

NEET Biology Evidence Of Evolution Morphological And Anatomical Evidence

Body Organisation. Body of all multicellular animals: cell organelles → cells → tissues → organs → systems.

Vertebrate Organs. Certain organs (for example Heart) show gradual modifications.

• Fish’s Heart. 2 chambered (1 auricle + 1 ventricle)
• Amphibian’s Heart. 3 chambered (2 auricles + 1 ventricle)
• Reptilian Heart. Incompletely 4 chambered (2 auricles + partly divided ventricle).
• A crocodile is a reptile, but it has a 4 chambered heart with completely divided ventricles.
• Mammals And Aves. 4 chambered hearts (2 auricles + 2 ventricles).

Homologous And Analogous Organs NEET Biology

Homologous Organs. Organs which look different and perform different functions but have the same basic structure and origin are called homologous organs. They are evidence in support of divergent evolution Examples,

1. Forelimbs of vertebrates such as seal (flipper), bat (patagium), horse (forelimb), man (arm).
2. Thom of ‘glory of the garden’ ( Bougainvillea) and tendril of Passiflora. Both look different and help in climbing in a different manner. But both arise in the axillary position and are modified branches.
3. Insect Legs. They are used in squatting in mosquitoes, collection of pollen in bees, clinging in lice, grasping in praying mantis and digging in mole cricket. However, in each case, it has five parts – coxa, trochanter, femur, tibia and 1-5 jointed tarsus.
4. Insect Mouth Parts. They have a labrum, two mandibles and two pairs of maxillae. Mouth parts are specialised for chewing and biting in cockroaches, chewing and lapping in Honey bees, sponging in Housefly, piercing and sucking in Mosquito and siphoning in Butterfly.

Differences in homologous organs are examples of divergent evolution/adaptive radiation. The occurrence of similar types of biomolecules in various groups of organisms is called molecular homolog}’, for example, blood proteins in humans and apes, hormones in mammals, and Rubisco in plants.

Analogous Organs. Organs which have the same function and look superficially alike but are quite different in fundamental structure and embryonic origin are called analogous organs and support convergent evolution. Examples,

1. Wing of an insect and that of a bat.
2. Fins of fishes and flippers of whales have similar functions and are structurally quite different,
3. Stings of Honey bee and Scorpion have similar functions but are modifications of the ovipositor and last abdominal segment respectively,
4. Photosynthesis is performed by different structures in Wild peas (stipules). Australian acacia (petiole) and Ruscus (cladodes).

Connecting Links are the living animals which possess the characteristics of two different groups of animals known as the connecting links. Examples

1. Lung Fishes — connecting link between fishes and amphibians.
2. Resemblance With Fishes — paired fins, gills and dermal scales.
3. Resemblance With Amphibians — internal nares, 3 chambered heart single or double lung for breathing.
4. Egg Laying Mammals — spiny ant eater, duck-billed platypus. Link mammals with reptiles.

Mammalian Features — hair, mammary glands, diaphragm, single aortic arch.

Reptilian Features — lay large eggs, presence of cloaca, large coracoid in pectoral girdle.

Some Other Connecting Or Missing Links

Missing links are the extinct animals which possess characters of two different groups of animals.

Fossil Evidence Supporting Evolution NEET Study Material

Vestigial Organs. The organs which occur in reduced form and are useless to the possessor, but correspond to the fully developed functional organs of their ancestors called vestigial organs. For example, the Human body has about 90 organs which are vestigial.

1. Tail Bone (Coccyx)
2. Wisdom Tooth
3. Nictitating Membrane. (Plica semilunaris) also called the third eyelid. Used in cats, eels, pigeons and frogs for cleaning the cornea. In men, this function is carried out by the upper eyelid.
4. Auricular Muscles. Three in mammals such as dog, cow, rabbit etc. ( Anterior, superior and posterior).
5. Caecum And Vermiform Appendix

Examples In Other Animals

1. Whales. Whales possess vestigial pelvic girdle and vestigial ear pinna (reduced).
2. Pythons and Boas possess vestigial, greatly reduced pelvic girdles.
3. The splint bones of horses represent the vestigial second and fourth toe.
4. Eyes have become vestigial in deep sea-dwelling animals like crayfish, salamanders etc.

Examples Of Vestigial Organs Of Plants. Leaves are reduced to scales in Ruscus and Asparagus. Pistil is reduced in ray florets of sunflower.

Atavism (Reversion ). It is the reappearance of certain ancestral (not parental) structures which have either completely disappeared or greatly reduced.

NEET Biology Evidence Of Evolution Embryological Evidences

Embroyological Evidence includes similar early development; similar vertebrate embryos, temporary embryonic structures; recapitulation theory and development of certain organs.

• Development of all triploblastic animals starts from a zygote and undergoes similar processes to form gastrula having-3 primary germ layers (ectoderm, mesoderm and endoderm) which have the same fate in organogenesis.
• Early embryos of different vertebrates are similar in having similar structures like gill slits, notochord, tail etc. and are indistinguishable from one another. All these support organic evolution.
• It is also supported by recapitulation theory by Von Baer (modified into Biogenetic Law by Haeckel) which states “Ontogeny repeats phytogeny” example, a tadpole larva of the frog.

NEET Biology Evidence Of Evolution Palaeontological Evidence

Palaeontological evidence includes missing links; distribution of fossils in the rocks of different periods, ancestries of animals etc.

• Vinci (1452-1519) is regarded father of palaeontology. Palaeontological evidences are based on a comparative study of fossils of different animals. Fossils are the remains or impressions of harder parts of past animals preserved in sedimentary rocks or other media.
• The age of the fossil is determined either by C¹⁴ – dating technique or the amount of lead in a rock.

Radioactive Carbon Method: The radioactive carbon method was discovered by W.F. Libby.

• Half half-life of radioactive carbon is 5730 years which was found in very minute quantity i.e. 0.1 % in the atmosphere and continuously produced from cosmic ray bombardment on earth’s upper atmosphere.
• Living organisms absorb radioactive carbon (C¹⁴) throughout their life from the environment in the form of CO₂ and organic molecules which signal death.
• After the death of organism, C¹⁴ began to decay according to its half-life i.e., 573 x 10³ years. It means 100 grams C¹⁴ will remain 50 grams in 5.73 x 10³ years and 25 grams in another 5.73 x 10³ years.
• By measuring the amount of C¹⁴ in a fossil relate this amount with the amount of C¹⁴ in a living organism, the age of the fossil can be estimated.
• This method is useful only to determine the age of actual remains and useless for moulds, casts or impressions.
• The C¹⁴ Radioactive carbon method can be used to determine the age of younger fossils that are not older than 70,000 years.
• This method is used for dating not only fossils but also archaeological remains.

Fossil Evidence Supporting Evolution NEET Study Material

Radioactive Clock Method: This method was discovered by Boltwood (1907) and is based on the disintegrating property of radioactive elements. These elements disintegrate at a steady rate into a stable substance for example in the U²³⁸ – Pb²⁰⁶ method the following decay takes place.

Uranium²³⁸  → Radium²²⁶ →Polonium²¹⁸ → Lead²⁰⁶ → Polonium²¹⁰ → Astatine²¹⁸

• One-half of uranium238 atoms will convert into Lead206 after 4.5 billion years (4.5 x 10¹⁰ years).
• The age of the rock can be calculated by estimating the uranium and lead quantity.
• This method is used for igneous rocks containing minerals and is useless for determining the age of sedimentary rock and fossils directly.

It is based on the fact that the older rock is less radioactive.

Potassium-argon Method: The transformation of radioactive potassium K⁴⁰ to argon and rubidium to strontium has been used for dating fossil-bearing rocks of any age and any type. Due to the greater concentration of potassium in most rocks, it is a more accurate method of dating fossils than uranium, a relatively rare element.

• It is the latest method to estimate the age of fossils.
• The half-life of potassium is 1.3 x 10⁹ years.
• Ordinary potassium contains 0.01 % of radioactive isotopes which disintegrate into calcium and argon.
• The age of the earliest known fossil of hominids in East Africa has been estimated by this method recently.
• It is possible to date very old rocks i.e. over three billion years by this method. Electron spin resonance dating

Electron Spin Resonance (ESR) dating is a relatively new, more precise and most accurate method of dating. It is based on the fact that background radiation causes electrons to dislodge from their normal positions in atoms and become trapped in the crystalline lattice of the material.

• When odd numbers of electrons are separated, there is a measurable change in the magnetic field (or spin) of the atoms.
• Since the magnetic field progressively changes with time in a predictable way as a result of this process, it provides another atomic clock or calendar, that can be used for dating purposes. ESR is used mostly to date Calcium carbonate in limestone, coral, fossil teeth, molluscs and egg shells. This method can date quartz and flint.
• This method has been used by palaeontologists mostly to date samples from the last 300,000 years.

1. Missing Links. They are those extinct organisms which had the characteristics of two different groups of animals. These also show the path of evolution. Archaeopteryx (lizard-bird) is a missing link between the reptiles and the birds.
   • They are the transitional forms between two present-day groups of organisms, for example, Pteridosperms (Pteridophytes and gymnosperms).
   • Toothed birds Reptiles and birds.
   • Archaeopteryx (Wagner 1861)
   • Reptilian Characters—toothed jaws, non-pneumatic bones, keel-less sternum, free caudal vertebrae, free clawed fingers.
   • Avian Characters—Fore limbs forming wings, feathers, beak, rounded cranium, fused skull bones.
2. Geological Succession Of Fossils shows that fossils have become more in number and show gradually increased complexity from the earliest to recent rocks.
   • Dinosaurs were highly flourished, giant reptiles of the Jurassic period (Age of Reptiles) of the Mesozoic era. These became extinct probably due to the direct hitting of a comet or a meteorite having rich amounts of iridium and global cooling.
3. Geological Time Scale is the tabulated form showing the sequence and duration of different eras and periods with their dominant form of life. It was proposed by Giovanni Avaduina (1760). It has 5 principal eras: Archaeozoic; Proterozoic; Palaeozoic; Mesozoic and Coenozoic. Another era is Azoic 4200- 4600 million years ago in which no life existed.
4. Phylogeny is the evolutionary history of an organism. The Palaeontologists have traced the ancestries of horses, elephants, camels etc. The evolution of horses started in North America about 60 million years ago.
   • The original dawn horse (Eohippus) has passed through stages like an intermediate horse (Mesohippus), ruminating horse (Merychippus) and Pliocene horse (Pliohippus) to transform into a modern horse (Equus).
   • These stages confirm the occurrence of changes like an increase in height, a reduction in the number of functional digits and an increase in the size of the crown of the molars.

NEET Biology Evidence Of Evolution Type Of Fossils

1. Unaltered. Woolly mammoth buried in ice.
2. Petrified. Replacement of organic parts by mineral
3. Moulds and casts
4. Prints. Footprints, prints of leaves, stems etc.

Types Of Rocks

1. Igneous Rocks. Rocks which are formed by the solidification of the original molten earth are called igneous rocks.
2. Sedimentary Rocks. Rocks formed due to deposition and subsequent stratification of soil particles over a long period of time are sedimentary rocks.
3. Metamorphic Rocks. These rocks are sedimentary rocks that are changed by heat and pressure.

In passing from the earliest to recent rocks, the fossils become more numerous and also progress from simple to more complex types.

Geological Time Scale

NEET Biology Evidence Of Evolution Biogeographical Evidence

1. Biogeography. The study of the distribution of animals and plants in the world is called biogeography.
2. Pangaea. It is held that around the carboniferous period ( about 375 million years back) or slightly earlier, all the present-day continents formed a single large irregular-level mass called Pangaea.
3. Realms Of Life. Sclater ( 1858) divided the earth into six realms for the distribution of birds while Wallace (1923) divided the earth into six realms for the distribution of both plants and animals.
   1. Nearctic
   2. Palaearctic
   3. Neotropical
   4. Oriental
   5. Ethiopian
   6. Australian
4. Discontinuous Distribution. Descendants of a common ancestor in some cases inhabit different continents and also differ from each other.
   1. Even with the same climate and topography, different realms have different types of flora and fauna. Central Africa has lions, elephants, antelope, and giraffes while Brazil has tapir, sloths, opossums, and llamas. The deserts of the two realms also differ with cacti in America and euphorbias in Africa. It is believed that at one time the whole land mass was one piece of Pangaea.
   2. About 200 million years back, it broke up into northern Laurasia and southern Gondwanaland. Laurasia further split up to form Eurasia, Greenland, and North America. Gondwanaland formed South America, South Africa, Australia, New Zealand and India.
   3. Another reorientation occurred 135 million years back when India was pushed upwardly to rest against Eurasia, South Africa joined North Africa and South America came close to North America.
      • The degree and period of separation of an area from another correspond to species diversity.
   4. Double coconut occurs only on Seychelles Island. Egg-laying mammals are restricted to Australia, Tasmania, and New Guinea. Kangaroo and Koala are marsupials found in Australia while Opossum is found in S. America.
   5. The two sides of the isthmus of Panama separated only a few million years back. They possess different but related species of invertebrates.
   6. Galapagos Islands is a group of 14 islands situated 800-960 km off the west coast of South America. Darwin visited the islands and called them living laboratories of evolution. The islands have 23 different species of birds and 11 types of tortoises.
   7. Amongst the birds are 14 species of finches (named Darwin’s finches by David Lach, 1947), a group of small birds which resemble the mainland seed-eating ground finches in general body pattern but differ in food habits, types of beaks, and several other physical features to appear distinct species.
   8. The finches must have come from the mainland but different islands of the Galapagos provided different types of environmental conditions so that the common stock became diversified due to genetic drift and adaptation to different food habits. It is an example of adaptive radiation/divergent evolution. Example,
      1. Alligators – occur only in the S.E. U.S.A. and Eastern China.
      2. Restricted Distribution. The parts separated from the rest of the world long have unique fauna and flora example, Australia.

Comparative Embryology In Evolution NEET Exam Preparation

NEET Biology Evidence Of Evolution Biochemical Evidences

1. Enzymes
2. Hormones
3. Blood proteins– of various mammals are similar to a large extent but are sharply distinguishable from those of other vertebrates. Man is nearest to the great apes (Chimpanzees and gorillas) and next in order are the old-world monkeys, the new-world monkeys and the tarsiers.
4. Molecular Homology. Similarity among animals at the molecular level is called Molecular Homology.

NEET Biology Evidence Of Evolution Cytological Evidence

All the living organisms are similar in being:

1. Cellular in nature and are formed of one (protozoans) or more cells (metazoans).
2. Presence of similar organelles having similar ultrastructure and functions.
3. All, the cells are formed of similar material called protoplasm having similar physical, chemical, and biological properties.
4. Basic metabolic cellular functions are performed similarly.

This supports that all the organisms are interrelated and have a common ancestry.

NEET Biology Evidence Of Evolution Comparative Physiology

All living organisms exhibit similarities in their chemical structure and function i. e., the biochemical composition and physiological activities, for example, the blood as regards cell and plasma, is markedly similar in different groups.

NEET Biology Evidence Of Evolution Genetics

The selection and interbreeding of domestic animals by man has led to the establishment of new races. This has been possible because of the changes occurring in genes producing mutations and variations in changed environments.

The natural forces of isolation and natural selection operate on these variations and some of them become heritable, leading to the formation of new races. The same process of gene mutation, variations, selection and interbreeding might have occurred on a large scale in nature leading to the establishment of new species.

Great Chain Of Being Or Aristotle’s Ladder Of Nature:

To express ideas about evolution various naturalists explained their different views. About 2000 years before Darwin explained his theory others expressed their views. According to Plato (428-348 BC), each species was an unchanging ideal form. All earthly representatives are imperfect imitations of such true essence of an ideal unseen world.

• As God is perfect, everything that existed on earth was His ideas. Later on, Aristotle (384-322 B.C.) further explained Plato’s idealistic concept to chain like a series of forms, each form representing a link in the progression from most imperfect to perfect. He called this chain as Ladder of Nature or Scala Naturae. It is also known as the “Great Chain of Being”
• Plate Tectonics: The concept of plate tectonics supposes that the surface layers of the Earth fit together like a spherical zig-zaw puzzle, and the individual pieces are on the move about one another.
• Continental Drift is the process in which it is supposed (from recent geological and other evidence) that the continental land masses have not always occupied their present position on the globe and that, powered by processes within the Earth itself, they are slowly and continuously on the move.
• In this way new land masses are created and destroyed, split apart and joined, over geological time. This hypothesis was first proposed by Snider in 1858 but developed by Taylor in America and Wagner in Germany in the late 1800s.
  • Significance. Continental Drift is one of the processes that can lead to geographical isolation.
• K-T Boundary. The boundary between rocks of the cretaceous and tertiary periods, about 65 million years, often having iridium and marketing the extinction of dinosaurs.
• Magma. It is the molten rock material present in the earth’s interior from which igneous rocks have been formed. Lava is also magma that has reached the surface of the crater of a volcano.
• Aeon Or Eon. It is the geological age consisting of one or more eras, viz., archaean, Proterozoic, and phanerozoic. Phanerozoic eon has three eras-palaeozoic, Mesozoic, and economic.

Comparative Embryology In Evolution NEET Exam Preparation

Evolution Of Horse:

The primary tendencies observed in equine evolution pertained to movement and alimentation.

They signify adaptations to fluctuating environmental conditions and can be summarized as follows:

• Augmentation in dimensions
• Elongation of extremities and feet
• Reduction of lateral digits.
• Augmentation in length and girth of the third digit
• Alignment and rigidity of the spine
• Enhanced sensory organs
• Expansion in size and intricacy of the brain correlated with the evolution of sensory organs.
• Broadening of incisors, substitution of premolars with molars, elongation of teeth, elevation of molar crown height, augmented lateral support of teeth through cement, and expanded cusp surface areas due to enamel ridge exposure.

The Basic Timeline Of A 4.6 Billion-Year-Old Earth, With Approximate Dates:

• 2 billion years of complex cells (eukaryotes),
• 1 billion years of multicellular life,
• 1000 million years of simple animals,
• 570 million years of arthropods (ancestors of insects, arachnids and crustaceans),
• 550 million years of complex animals,
• 500 million years of fish and proto-amphibians,
• 475 million years of land plants,
• 400 million years of insects and seeds,
• 360 million years of amphibians,
• 300 million years of reptiles,
• 200 million years of mammals,
• 150 million years of birds,
• 130 million years of flowers,
• 65 million years since the dinosaurs died out,
• 2.5 million years since the appearance of the genus Homo,
• 200,000 years of anatomically modern humans,
• 25,000 years since the disappearance of Neanderthal traits from the fossil record.
• 13,000 years since the disappearance of Homo floresiensis from the fossil record.

NEET Biology Evidence Of Evolution Synopsis

Mammals among animals and angiosperms among plants are the most advanced forms. The earliest era in the geologic record is Precambrian.

Phylogenetics = Cladistics. Some workers in cladistics equate homology with synapomorphy. In molecular biology, the term indicates a significant degree of sequence similarity between D.N.A. or protein sequences.

• Evolved from common ancestor = Monophyletic origin
• Dundee. It is the famous city of fossils in Italy
• Unaltered fossils of 25, 000 yrs old elephant woolly mammoths were found in ice of Siberia (Russia)
• Evolution Is Irreversible. Also called Dollo’s law (Dollo, 1893).
• Cope’s Law. In the course of evolution, there is a tendency for animals to increase in size.
• Bergman’s Law. Warm-blooded animals are larger in size in the colder regions as compared to hotter parts.
• Allen’s Law. Extremities like tails and ears become smaller in colder areas.
• Gloger’s Rule. Warm-blooded animals have more melanin in hot wet areas but develop yellow-red pigment in hot dry areas.

Paleontological Evidence Of Evolution NEET Preparation

Ontogeny Repeats Phylogeny

Recapitulation theory – Karl Von Baer

Biogenetic Law – Ernst Haeckel

• Biogenetic Law can be illustrated even with an example amongst plants. Seedlings of Acacia tree initially develop simple leaves which later transform into compound leaves. Another example is that modern-day oaks of the southern U.S.A. retain their foliage throughout the year whereas the oaks of the northern United States are deciduous and shed their leaves during winter.
• Dinosaurs. Extinct reptiles were of two types, lizard-hipped (order Saurischia) and bird-hipped (order ornithischian), originated about 230 million years back, both carnivorous and herbivorous, using four or two legs, brain small as compared to body, often with a long tail, smallest, with size of chicken (Compsogncithus) and the largest Brachiosaurus reaching 12.6 m and weighing 80 tonnes (some workers believe that the largest dinosaur was Apatosaurus = Brontosaurus that reached a length of 21 m having a weight of 30 tonnes). The teeth of carnivorous Tyrannosaurus were 16 cm long. Plesiosaur and Pilosaur are marine reptiles of the Jurassic and Cretaceous period.

The main factor responsible for the mass extinction of dinosaurs is suggested to be the hitting of the earth by a comet or a meteorite with rich amounts of metal- iridium. Another hypothesis, suggested for this mass extinction, is ‘global cooling’

• Pterosaurs are extinct flying reptiles of the Mesozoic age. Some of them had a wing span of 12 m.
• Synapsids/Synapsida. Mammal-like reptiles of carboniferous to Triassic (315-195 million years). Some of them gave rise to mammals (for example, Pelycosaurs and Therapsids). Synapsids were eliminated by dinosaurs.
• Convergence. Development of similarities between animals or plants of different groups resulting from evolution to similar habitats
• Latimeria (Coelocanth) is a lobe-finned (Cross- opterygian) fish in which fins arise from limb-like stalks and not directly from the body. It is the oldest living fish and once was believed to have become extinct about 70,000,000 years ago.

It is regarded as a “living fossil” as it has lived till today without undergoing any change in it. Other living fossils are Antedon (Feather star – echinoderm); Limulus (king crab -an arachnid); Cycas, etc.

• George Cuvier (1769 – 1832). Proposed the theory of catastrophism. Founder/father of modern palaeontology.
• Leonardo de Vinci ( 1452-1519). Father of palaeontology.
• The fossil-like impressions formed on certain rocks due to the deposition of minerals in rock crevices are called pseudofossils.
• The large-scale extinction of plants and animals within a short period is called mass extinction.
• Triassic. An epoch between 181 -225 million years ago with dry climate. Sandstone rocks are common. First mammals appeared.
• Palaccology. It deals with the study of ancient organisms and their environment.
• Hoofed animals like horses originated in the Eocene epoch in North America.
• Igneous rocks are devoid of fossils.
• A thorn of Bougainvillea and tendril in Cucurbita: Homologous

NEET Biology Evidence Of Evolution Multiple Choice Questions And Answers

Question 1. Homologous organs are:

1. Constructed on a similar plan of organization and embryonic development
2. Morphologically similar
3. Functionally identical
4. None of the above.

Answer: 1. Constructed on a similar plan of organization and embryonic development

Question 2. Analogous organs are those which are:

1. Structurally identical
2. Functionally similar
3. Both structurally and functionally resemble each other
4. Normally not functional.

Answer: 2. Functionally similar

Question 3. One of the following is not a vestigial organ:

1. Vermiform appendix
2. Wisdom tooth
3. Epiglottis
4. Scalp hair.

Answer: 3. Epiglottis

Evolution Zoology NEET Practice Questions MCQs Question 4. Biogenetic law was given by:

1. Hooke
2. Hymen
3. Haeckel
4. Darwin.

Answer: 3. Haeckel

Question 5. Vestigial organs are those:

1. Which were functional long ago but became non-functional now
2. Rudimentary in development
3. Degenerated now
4. Functional at present but reduced.

Answer: 1. Which were functional long ago but became non-functional now

Question 6. The earliest age in the geological record is:

1. Cenozoic
2. Precambrian
3. Palaeozoic
4. Mesozoic.

Answer: 2. Precambrian

Question 7. The Carboniferous period during which amphibians flourished occurred approximately:

1. 25 million years ago
2. 135 million years ago
3. 345 million years ago
4. 500 million years ago.

Answer: 3. 345 million years ago

Read and Learn More NEET Biology Multiple Choice Question and Answers

Question 8. The Permian period, during which most modem orders of insects appeared, occurred approximately:

1. 80 million years ago
2. 135 million years ago
3. 280 million years ago
4. 550 million years ago.

Answer: 3. 280 million years ago

Evolution Zoology NEET Practice Questions MCQs Question 9. Macroevolution is the evolution of:

1. Macromolecules
2. Phylogenetic gaps
3. Major events occurring over geologic time
4. Large organisms.

Answer: 3. Major events occurring over geologic time

Question 10. A structure, such as a feather that evolved in one context and was then used for a completely new function is a:

1. Mystery to macro evolutionists
2. Pre-adaptation
3. Macrostructure
4. Paedomorphs.

Answer: 2. Pre-adaptation

Question 11. Retention in an adult organism of juvenile features of its ancestor is known as:

1. Allometiy
2. Preadaptation
3. Macro-development
4. Paedomorphosis.

Answer: 4. Paedomorphosis.

Question 12. The wings of a bird and the forelegs of the horse are:

1. Analogous organs
2. Homologues
3. Vestigial structure
4. Phylogenetic structure.

Answer: 2. Homologues

Question 13. The pelvis and the leg bones of a snake are:

1. Analogous organs
2. Homologous structures
3. Vestigial structure
4. Phylogenetic structure.

Answer: 3. Vestigial structure

Question 14. The best test of the relatedness of the species is in the similarity of their:

1. Anatomy
2. DNA and proteins
3. Development
4. Courtship behaviour.

Answer: 2. DNA and proteins

Question 15. George Cuvier realized that the history of life is recorded in fossils and believed that replace of one species by another is caused by:

1. Massive number of mutations
2. The wrath of God
3. Extinctions due to catastrophes such as floods
4. Genetic inbreeding.

Answer: 3. Extinctions due to catastrophes such as floods

Question 16. Most fossils are found in:

1. Granite
2. Sedimentary rocks
3. Lava flows
4. Black soil.

Answer: 2. Sedimentary rocks

Evolution Zoology NEET Practice Questions MCQs Question 17. Of all the living species that ever lived approximately how many have gone extinct?

1. Less than 1%
2. 20%
3. 60%
4. More than 99%.

Answer: 4. More than 99%.

Question 18. For the origin of life, most important condition is:

1. H₂O
2. Carbon
3. Nitrogen
4. Free oxygen.

Answer: 1. H₂O

Question 19. The richest source of fossils is:

1. Basalt
2. Granite
3. Lava
4. Sedimentary rocks.

Answer: 4. Sedimentary rocks.

Question 20. The fossil animals which show characters of two different groups of animals are called as:

1. Extinct animals
2. Missing links
3. Vestigial animals
4. None of these.

Answer: 2. Missing links

Question 21. The Haeckel’s theory of recapitulation (Biogenetic Law) means that:

1. All organisms start as an egg
2. Life history of an animal reflects its evolutionary history
3. The progeny of an organism resembles its parents
4. Body parts once lost are regenerated.

Answer: 2. Life history of an animal reflects its evolutionary history

Question 22. Who established the precipitation method of blood tests for finding out the inter-relationship among different animals:

1. Haeckel
2. Foxon
3. L. De Vinci
4. H.F. Nuttal.

Answer: 4. H.F. Nuttal.

Question 23. The connecting link between chordates and non- chordates is:

1. Peripatus
2. Balanoglossus
3. Sphenodon
4. Tachyglossus.

Answer: 2. Balanoglossus

Evidences for Evolution MCQ  Question 24. Which of the following would be easily fossilized?

1. External ear
2. Heart
3. Skin
4. Tooth.

Answer: 4. Tooth.

Question 25. Which of the following is a living fossil?

1. Euglena
2. Balanoglossus
3. Sycon
4. Limulus.

Answer: 4. Limulus.

Question 26. The archaeozoic era is considered as the age of:

1. Protista
2. Marine life
3. Amphibians
4. Fishes.

Answer: 1. Protista

Question 27. Geologically one of the following eras is known as the ‘Age of Reptiles’ or the ‘Golden Age of Dinosaurs.’

1. Palaeozoic
2. Cenozoic
3. Mesozoic
4. Psychozoic.

Answer: 3. Mesozoic

Question 28. Appearance of teeth in the embryos of birds is an example of:

1. Vestigial organs
2. Ontogeny repeats phylogeny
3. Atavism
4. Speciation.

Answer: 2. Ontogeny repeats phylogeny

Question 29. Archaeopteryx is a missing link between:

1. Reptiles and birds
2. Reptiles and mammals
3. Birds and mammals
4. None of these.

Answer: 1. Reptiles and birds

Question 30. Dinosaurs are extinct:

1. Reptiles
2. Mammals
3. Birds
4. Amphibians.

Answer: 1. Reptiles

Question 31. Some of the important evidences of organic evolution are:

1. Occurrence of homologous and vestigial organs
2. Occurrence of analogous and vestigial organs
3. Occurrence of homologous and analogous organs
4. Occurrence of analogous organs only.

Answer: 1. Occurrence of homologous and vestigial organs

Evolution MCQ For NEET Biology With Answers Question 32. Which of the following is not a vestigial organ in man?

1. Vermiform appendix
2. Plica semilunaris
3. Ear muscles
4. Epiglottis.

Answer: 4. Vermiform appendix

Question 33. Which of the following are the examples of analogous structures?

1. Leaves of a plant and cladodes of Ruscus
2. Wings of an insect and wings of bird
3. Hands of man, monkey and kangaroo
4. Both (1) and (2).

Answer: 4. Both (1) and (2).

Question 34. Blood groups A, B, AB and O occur in humans. The blood groups A and B are found in apes but not in monkeys. This suggests that:

1. Humans, monkeys and apes are related
2. Human beings are more closely related to apes
3. Human beings are more closely related to monkeys
4. Human beings are more closely related to apes than to monkeys.

Answer: 4. Human beings are more closely related to apes than to monkeys.

Question 35. Which one of the following is homologous?

1. Tails of scorpion, bird and monkey
2. Stings of bees, scorpions and fangs of monkey
3. Wings of butterflies, flying fish and bird
4. Paddles of whale, antis of man and wings of bat.

Answer: 4. Paddles of whale, antis of man and wings of bat.

Question 36. Which of the following illustrates palaeontological evidence in favour of organic evolution?

1. Archaeopteryx
2. Peppered moth
3. Duck-billed platypus
4. Darwin’s finches.

Answer: 1. Archaeopteryx

Question 37. Evolutionary changes occurring in distantly related organisms are classified as:

1. Parallel evolution
2. Divergent evolution
3. Convergent evolution
4. Macro-evolution.

Answer: 3. Convergent evolution

Evolution MCQ For NEET Biology With Answers Question 38. Which of the following are homologous?

1. Passijlora tendril and Bougainvillea thorn
2. Insect wing and bird wing
3. Tortoiseshell and mollusc shell
4. Sweet potato and Ginger.

Answer: 1. Passijlora tendril and Bougainvillea thorn

Question 39. Which of the following is an extinct animal?

1. Protopterus
2. Columba
3. Archaeopteryx
4. Equus.

Answer: 3. Archaeopteryx

Question 40. A fossil is a:

1. Laboratory preserved animal
2. Dead animals of the past
3. Organic relic of the past
4. Stuffed animal of the past.

Answer: 3. Organic relic of the past

Question 41. Which of the following is the vestigial organ in man?

1. Vermiform appendix
2. Cervical vertebrae
3. Atlas vertebra
4. None of the above.

Answer: 1. Vermiform appendix

Question 42. Successful adaptation simply means:

1. An increase in fitness
2. Producing viable offspring
3. Evolving new characters
4. Moving to a new place.

Answer: 2. Producing viable offspring

Question 43. The law of superposition is associated with:

1. Vision in arthropods
2. Study of fossils
3. Inheritance
4. All of the above.

Answer: 1. Vision in arthropods

Question 44. How many million years is the age of the oldest rock on earth

1. 3500
2. 20
3. 5000
4. 4500.

Answer: 1. 3500

MCQ Evidences for Evolution Question 45. Fossil of Archaeopteryx is placed in:

1. Moscow
2. New York
3. London
4. Vienna.

Answer: 3. London

Question 46. Which of the following is the most primitive mammal?

1. Spiny anteater
2. Scaly anteater
3. ArmadiWo
4. Seal.

Answer: 1. Spiny anteater

Question 47. Birds of Galapagos island were named as Darwin’s finches by:

1. Wallace
2. Darwin
3. Dr David Lach
4. Empedocles.

Answer: 3. Dr David Lach

Question 48. Which one of the following groups are not analogous organs?

1. Wings of birds and wings of butterflies
2. The eye of octopus and eye of mammals
3. Flippers of penguins and flippers of dolphin
4. Thoms of Bougainvillea and tendril of Cucurhila
5. Tuberous roots of sweet potato and stem tuber of potato

Answer: 2. The Eye of octopus and the eye of mammal

Question 49. Haeckel’s recapitulation theory was based on:

1. Germ layers
2. Germplasm
3. Genetic variation
4. None of the above.

Answer: 1. Germ layers

Question 50. The dating of rocks is done by calculating the ratio between which of the following pairs in the igneous rocks associated with sedimentary rocks:

1. Uranium—Lead
2. Potassium-Argon
3. Rubidium —Strontium
4. All the above.

Answer: 4. All the above.

NEET Biology Origin Of Life

Life– The inherent capacity of organisms to utilise outside materials for energy, growth and reproduction through chemical reactions. Life is regarded as a power that an organism possesses to maintain and produce itself.

Big Bang Theory – A single huge explosion

• The universe expanded → Temperature came down – Hydrogen and Helium formed later on.
• Gases condensed under gravitation and formed galaxies of the present-day universe.
• Earth formed almost 4.5 billion years ago.
• No atmosphere on early Earth.
• Water vapours, methane, CO₂, NH₃ released from molten mass covered the surface.

UV rays of the sun broke up.

Read and Learn More NEET Biology Notes

Oxygen is combined with ammonia, and methane to form water CO₂ and other simple molecules.  An ozone layer was formed.

Biopoiesis – the process by which life originated.

According to the Cosmozoic theory developed by Richter and supported by Thomson, Helmholtz and Arrhenius states that life (protoplasm) reached the earth in the form of spores or germs from outer space.

Origin Of Life NEET Notes

Theory of special creation—By Father Suarez.According, to it life was created by super supernatural power in 6 days.

• 1st day — he made heaven and earth
• 2nd day—separated sky from water
• 3rd day—dry land of plants
• 4th day—Sun, moon and stars
• 5th day—Birds and fishes
• 6th day—Land animals and human beings.

Theory of eternity of Life—By Richter (1865), Preyer (1880), Helmholtz (1884), Arrhenius (1908), Moyle (1950), Bonds (1952).

According to it, “Life is immortal”. Living matter has occurred in association with non-living matter from the beginning. Thus according to this theory, Life changes its form and it was never created.

• According to spontaneous generation theory, life originated from non-living things. It is estimated that life originated approximately 3,600 million years ago.
• Scientists supporting this theory— Aristotle, Van Helmont, William Harvey, Haeckel, Plato, Xanophanes, Thales, Anaximander, Empedocles
• Experimental support was provided by the Van Helmont experiment (1642).
• Abiogenesis was challenged on the basis of experiments by—Francisco Redi and Spallanzani. Finally disapproved by – Louis Pasteur.

Biogenesis. The fact that new life (nowadays) comes from any pre-existing life (Omne vivutn exvivo).

Theory Of Catastrophism. It states that there have been several creations each preceded by a catastrophe due to some geological disturbance. Each catastrophe completely destroyed life and each creation consisted of life quite different from that of the previous one. (George Cuvier and Orbigney)

Origin Of Life NEET Notes

Oparin-Haldane Theory (Naturalistic, Chemical or Heterotroph Theory)

A.I. Oparin and J.B.S. Haldane’s (1936)

The theory of the “Origin of Life” is widely acknowledged.

• Life emerged by chemical evolution, as the primordial Earth’s atmosphere was decreasing, characterized by elevated temperatures and the presence of gases like as nitrogen, hydrogen, methane, ammonia, and water vapor.
• As the temperature decreased, certain gasses condensed into liquids, while some liquids solidified. Free oxygen was nonexistent.
• Extensive polymers, including proteins, nucleic acids, and other molecules, were methodically synthesized by the influence of high-energy solar radiation, energy from alternative sources (likely isotopes on primordial Earth), and energy from electrical discharges.

The main steps of the theory are as follows:

• The first organisms were heterotrophs and anaerobic containing nucleoproteins which gave rise to autotrophs.
• Universe – 15-20 bya (Billion years ago.)
• Earth – 4.5/4.6 bya
• Life 4.0 bya (life appeared 500 mya after the formation of the earth)
• Non-cellular form of life may have originated 3 by (RNA + Protein + Polysaccharides)
• Cellular form of life 2000 mya(million years ago)
• Life was present on earth about 3.9 bya.
• Microfossils of cyanobacteria appeared 3.3 to 3.5 bya.
• Origin of Eukaryotic cell – 1.5 bya.

NEET Biology Origin Of Life Some Early Contributors To The Knowledge Of Evolution And Related Topics

Thales (624-548 B.C.): A Greek who proposed a theory that water (ocean) was the mother of all life.

Anaximander (611—547 B.C.): A Greek who thought that life arose from a mixture of water and earth and that landforms arose from aquatic types, particularly under the influence of the sun’s heat.

Heraclitus (510—450 B.C.): A Greek natural philosopher who stated that “struggle is life” and “all is flux”— thoughts that are basic to modem ideas in evolution.

Empedocles (495-435 B.C.): A Greek who theorized that living organisms were generated spontaneously from scattered materials, being attracted by love and hate.

“Founder of the concept of organic evolution”

Aristotle (384-322 B.C.): A Greek who theorized that in the living world, there was a gradual change from the simple and imperfect to the more complex and perfect, thus suggesting the idea of evolution.

Saint Augustine (353-439 A.D.): Saint Augustine interpreted the first chapter of Genesis, stating that in the beginning matter was created with the properties and potentialities to evolve into living and non-living worlds as we know them today.

Origin Of Life NEET Notes

Leonard de Vinci (1412-1529) “Father of Palaeontology”

Francisco Redi (1621-1697): An Italian who overthrew the theory of spontaneous generation, which stated that life arose from non-living materials spontaneously, by discovering that eggs and larvae of insects originated from previous living insects, rather than from non-living substances.

Carl Linnaeus: Father of taxonomy

Giovanni Avadeuna (1760) proposed Geological time scale

Thomas’ Robert Malthus (1766-1834): An English economist whose “Essay on Population,” published in 1798, inspired both Darwin and Wallace in their theories of evolution.

Charles Lyell (1797-1875): A Scottish geologist who laid the foundations for the science of earth structure in his Principles of Geology (1830-1832). He is considered an important contributor to the theory of organic evolution because of his influence on Charles Darwin and Alfred Russel Wallace.

Georges Cuvier (1769-1832): A Frenchman who supported the “Cataclysmic Theory,” in which he stated that there had been numerous creations, each of which was followed by a cataclysm (catastrophe) that destroyed it, and its place was taken by new forms. He is regarded as the founder/father of modern palaeontology

Georges de Buffon (1707-1788): A French naturalist who excluded the possibility that species have the ability to evolve (change). He probably was influenced by the ancient ideas revived during the Renaissance that discredited such a possibility.

Charles Bonnet (1720-1793): A Swiss naturalist and philosopher who first used the term “evolution” but not quite as we do today, and conceived that organisms could be arranged in a ladder-like, linear series.

Erasmus Darwin (1731-1802): An English evolutionist who was the grandfather of Charles Darwin. He believed that acquired traits could be transmitted to future generations and he may have influenced Lamarck, who had similar views.

Jean Baptiste Lamarck (1744-1829): A French biologist who was a student of organic evolution. He believed that environmental influences, and the effects of the use and disuse of body parts, were causes of evolutionary changes—a theory that laid the foundation for the “Theory of the Inheritance of Acquired Traits.”

Charles Darwin (1809-1882): Darwin, on a voyage around the world in the sailing ship HMS Beagle, indicated the descent of species by the development of varieties from common stocks. This process entailed a “struggle for existence,” which resulted in a “natural selection of species” and a “survival of the fittest.” He wrote The Origin of Species by Means of Natural Selection (1859).

Origin Of Life Class 12 NEET Solutions

Thomas Henry Huxley (1825-1895): An English surgeon who actively supported the views of Charles Darwin and assisted in promoting them extensively.

Alfred Russel Wallace (1823-1913): An Englishman who studied animal geography in the East Indies and concluded that the life of wild animals is a struggle for existence. He worked on the problem of the origin of species and arrived at conclusions concerning evolution that resembled those of Charles Darwin.

Louis Pasteur (1822-1895): A French microbiologist and chemist who proved that only living organisms such as bacteria and yeasts could cause fermentation. He proposed a method of preventing this process by heating to a temperature high enough to kill the germs. This method is known as pasteurization. Pasteur’s work ended the controversy regarding the possibility of the spontaneous generation of living organisms from non-living materials.

August Weismann (1834-1914): A German who distinguished between body cells and germ cells and proposed the “Theory of the Continuity of Germplasm from Generation to Generation” (1885). He opposed the idea that acquired traits might be transmitted.

Mendel’s work published (1866)—(Unknown to Darwin)

Henry Walter Bates (1825—1913). Proposed the concept of Batesian mimicry in 1862.

J Fritz Muller (1821—1897). Described in 1879 the Mullarian mimicry.

Scaler (1858) divided the earth into six realms for the distribution of birds,

Richard Leaky (1930). Modem Palaeontologist

Lewis and Leaky (1955) excavated fossil forms of Ramapithecus and Kenyapithecus

Origin Of Life Class 12 NEET Solutions

Lucy, C. Johanson (1981) American anthropologist discovered the complete skeleton of a 30-35 lakhs years female fossil hominid resembling Australopithecus

Eugene Dubois (1891) excavated a fossil of Homo erectus erectus

Laplace (1749—1827) proposed a nebular hypothesis to explain the origin of the solar system

Horowitz suggested that the earliest form of life was in the form of naked gene

Solar System. Sun along with orbiting planets and their satellites, the comets and asteroids constitute the solar system.

Origin Of The Solar System. The solar system originated from the gravitational contraction (condensation) of a solid cosmic cloud and dust called a nebula.

• During condensation, this cloud began to rotate due to the initial velocities of particles brought together. The condensation and spin continued. Thus most of the mass is concentrated near the centre. The flattened discs broke into a number of whirling masses of smaller clouds. The sun was formed from the central dense part.
• The sun started radiating energy. The other planets including the Earth were formed from the cooler, less dense outer regions almost in the same plane.

Cosmology. The study of heavenly bodies and the cosmos is called cosmology. The major theories of the origin of the universe are chemical origin and the Big Bang is the most accepted theory about the origin of the universe.

According to the Big Bang theory universe came into existence some 19 billion years ago by a thermonuclear explosion, called the Big Bang, or a dense entity will eventually contract again. Sun and its planets including Earth came into existence at the same time from a common source.

Origin Of Life Class 12 NEET Solutions

Two Major Events Of The History Of Life Are:

1. Origin of life (biopoiesis).
2. Evolution of life.

The Major Theories Of the Origin Of Life Are:

1. Special Creation (Proposed by Father Saurez). This theory of special creation attributes the origin of life to a supernatural or vitalistic event at a particular time in the past. In other words, this theory believes in the creation of life by God.
2. Spontaneous Generation. (Concept held by Thales, Anaximander, Empedocles, plants). This theory discards abiogenesis and believes in the biogenetic origin of life i.e. life originates from pre-existing life-biogenesis.
3. Extraterrestrial or Cosmic Origin (Richter). This theory believes that life on Earth came from some other planet.
4. Terrestrial Origin or Abiogenic Origin (Oparin and Haldane). This theory states that life originates on Earth from collections of organic molecules that were produced early in the history of Earth.

This theory of terrestrial origin has a scientific base.

Role Of Catalytic Rna In Origin Of Life

1. The precursor of RNA of ciliate protozoan, Tetralymena was found to contain a self-splicing intron-containing 413 nucleotides which act as enzymes,
2. The very first living molecule might have been an RNA replicase that catalysed its own replication without the help of a protein.
3. Catalytic RNA are now considered to be molecular fossils.

• Biogeny. Origin of first life.
• Chemogeny. Origin and evolution of organic chemicals.
• Cognogeny Is The Evolution of different forms of living species.
• Biopoiesis. Origin of life.
• Biogenesis. Origin of life from life.
• Continental Drift Theory. Proposed by Wagener (1912) that about 250-200 million years there was a single land mass or continent which subsequently got split into continents as are known today.

Plate Tectonics:

John Tujo Wilson (1965) posited that the Earth’s outer surface comprises a mosaic of thick plates, both large and small, with a thickness of 70-100 km, which move in relation to one another, perhaps due to convection currents in the semi-molten mantle underneath.

• This movement is thought to have commenced approximately 2000 million years ago at a velocity of 6 centimeters per year. As a result, the continents are gradually rotating around the Earth. They have previously accomplished this four times.
• Francisco Redi denied the spontaneous creation of flies from decaying flesh in 1668.
• The energy radiated by the sun originates from nuclear fusion events.
• The initial kind consists of seas created from atmospheric water.
• Clay is optimal for the concentration of monomers. cs Cells with extended metabolic pathways were favored as primitive cells depleted the directly usable organic compounds.
• The most ancient fossilized cells resemble heterotrophic bacteria.
• The primordial autotrophs were likely anaerobic chemoautotrophs.
• The initial creatures to emit oxygen were likely cyanobacteria.

NEET Biology Origin Of Life Synopsis

The study of the universe or cosmos is called cosmology.

• Exobiology. Investigation of life on heavenly bodies other than the earth.
• The first organisms were — Heterotrophs. (Chemo- heterotrophs).
• Age of the earth – 4600 million yrs.
• Earliest prokaryotes – 3600 million yrs.
• The first formed compounds were probably – proteins and nucleic acids.
• Aristotle – The first proponent of the theory of abiogenesis.
• Origin of life – somewhere between 4.5 x 10⁸ to 3.6 x 10⁸ years ago.
• Origin of life – in water (probably sea).
• Gas is absent in the primitive atmosphere – free oxygen.

Gases present in the primitive atmosphere – N₂, CH₄, H₂, NH₃, H₂O_(g)

• Spontaneous generation (Abiogenesis) theory was proposed by Van Helmont (1577—1644) and the concept was supported by – Thales, Xanophanes, Empedocles, Plato, and Anaximander.
• Empedocles is regarded as the father of evolutionary concepts.
• Spontaneous generation theory challenged by – Fran-cisco Redi, Spallanzani and Pasteur Tyndall
• No life on the moon as there is no atmosphere on the moon because of the low escape velocity on the moon in which gas molecules easily cross.
• A.I. Oparin wrote a book “Genesis and Evolutionary Development of Life” and “Origin of Life” on Earth.
• “Evolution from Space” was written by Fred Hoyle.
• F.H.C. Crick (1982) published a book with the title ‘Life itself’.
• Cosmozoic theory of the origin of life was proposed by Richter and supported by Arrhenius.

Sydney W. Fox. discovered aqueous suspension of polymers’ spherical aggregates. He called the coacervates a microsphere.

• S.W Fox demonstrated that if a nearly dry mixture of amino acids is heated, polypeptide molecules are formed.
• Melwin Calvin (1951) strongly irradiated CO₂ and H₂ in a cyclotron to form formic acid, succinic acid and oxalic acid.
• J.B.C. Haldane bom on 5 Dec. 1897 in England. He shifted to India in July 1957 and settled in Bhubnashwer. He died on 1st Dec. 1964. He was a biologist, biochemist and geneticist.
• Louis Pasteur gave “Germ Theory of Disease and Immunology.”
• Progenote is regarded as early single-celled common ancestors of archaebacteria, eubacteria and eukaryotes. Thus, no present-day bacterial type can be regarded as an ancestor of eukaryotes.

NEET Biology Origin Of Life Of Earth

The genesis of life is associated with the inception of Earth, the Cosmos, and the Universe, which emerged 10 to 20 billion years ago due to the Big Bang (a thermonuclear explosion). A galaxy, such as the Milky Way, consists of billions of stars, including our Sun, together with its respective planets and satellites.

• The solar system comprises the sun, its planets, and their satellites.
• Earth is the third planet, characterized by its rocks, water, and atmosphere. It commenced as gaseous clouds of metallic and non-metallic atoms, subsequently condensing to create surface rocks, a boiling fluid core, and a gaseous atmosphere.
• Cosmology. Investigation of the cosmos.
• The oldest extant rock is 4.3 billion years old and contains no evidence of life.
• 3.9 billion-year-old rocks contained carbonates indicative of biological activities.
• The most ancient microfossils of Cyanobacteria date back 3.3 to 3.5 billion years.
• Francis Crick and Leslie Orgel suggested the notion of guided panspermia, which was substantiated by genetic code and the function of the metal molybdenum.

NEET Biology Origin Of Life Multiple Choice Questions And Answers

Question 1. Life has originated due to:

1. Creation by god
2. Effects of sunshine on mud
3. Spontaneous generation
4. None of the above.

Answer: 4. None of the above.

Question 2. On one of the planets life has originated approximately some:

1. Half billion years ago
2. One billion years ago
3. Two billion years ago
4. Four billion years ago.

Answer: 4. Four billion years ago.

Question 3. The branch of zoology dealing with similarities and differences between individuals related by descent is:

1. Evolution
2. Ecology
3. Eugenics
4. Genetics.

Answer: 1. Evolution

Question 4. The spontaneous generation theory was first refuted by:

1. S.L. Miller
2. F. Redi
3. L. Spallanzani
4. L. Pasteur.

Answer: 2. F. Redi

Origin of Life Recommended MCQs – NEET Questions  Question 5. According to one of the most widely accepted theories, the earth’s atmosphere before any life had originated on this planet consisted of a mixture of:

1. Hydrogen, carbon dioxide, ammonia, oxygen
2. Ozone, methane, oxygen and water vapour
3. Water vapour, hydrogen, ammonia and methane
4. Oxygen, hydrogen, methane and ammonia.

Answer: 3. Water vapour, hydrogen, ammonia and methane

Question 6. Pasteur is famous for

1. Rejection of spontaneous generation theory
2. Cell theory
3. Vaccination
4. Both (1) and (3).

Answer: 4. Both (1) and (3).

Question 7. There is no life on the moon as there is no:

1. Nitrogen
2. Oxygen
3. Carbon
4. Water.

Answer: 4. Water.

Question 8. In the field of discovery of the origin of life, Miller prepared:

1. Ammonia
2. Protein
3. Amino acids
4. Hydrogen.

Answer: 3. Amino acids

Read and Learn More NEET Biology Multiple Choice Question and Answers

Question 9. Large colloidal particles containing protein with water molecules are:

1. Microsphere
2. Coacervates
3. Spherules
4. All of the above.

Answer: 4. All of the above.

Question 10. The energy source for the origin of life came from:

1. Ultraviolet light
2. Electric charge
3. High temperature
4. All the above.

Answer: 4. All the above.

Question 11. Which of the following were first formed?

1. Eobionts
2. Coacervates
3. Genes
4. Cells.

Answer: 2. Coacervates

Question 12. The first organisms were:

1. Autotrophs
2. Hctcrotrophs
3. Saprotrophs
4. None of the above.

Answer: 2. Hctcrotrophs

Question 13. Which of the scientists is associated with the naturalistic theory of the origin of life?

1. Pasteur
2. Oparin
3. Miller
4. Redi.

Answer: 2. Oparin

Question 14. Which is the most accepted theory of the origin of life

1. Theory of special creation
2. Theory of spontaneous generation
3. Oparin-Haldane theory
4. Theory of eternity of life.

Answer: 3. Oparin-Haldane theory

Question 15. Miller synthesized simple amino acids from:

1. H₂, NH₃, HCN and O₂
2. H₂, NH₃, CH₄ and water vapours
3. NH₃, CH₄, HCN
4. H₂, O₂, N₂ and H₂O.

Answer: 2. H₂, NH₃, CH₄ and water vapours

Evolution MCQs Question 16. The theory of special creation envisages the role of:

1. Chemical evolution
2. Abiogenesis
3. Divine intervention
4. Physical accretion.

Answer: 3. Divine intervention

Question 17. The theory of catastrophism considers one of the following as its mainstay:

1. That the earth was periodically devastated by catastrophes causing drastic changes
2. Catastrophic events eliminate life form
3. Does not support the theory of special creation
4. Elimination is the end of all events.

Answer: 1. That the earth was periodically devastated by catastrophes causing drastic changes

Question 18. The branch of Biology dealing with the study of the distribution of organisms in different geographic regions is:

1. Biogeography
2. Ecology
3. Eugenics
4. Genetics.

Answer: 1. Biogeography

Question 19. ‘Origin of Life’ hypothesis was initiated by:

1. Mendel
2. Darwin
3. Oparin
4. Pasteur.

Answer: 3. Oparin

Question 20. The atmosphere of the earth at the time of the origin of life was:

1. Oxidising
2. Reducing
3. Neither oxidising nor reducing
4. Having very low temperature.

Answer: 2. Reducing

Question 21. According to Oparin, the universe was a vast dense cloud of hot gases:

1. 7-10 billion years ago
2. 5-7 billion years ago
3. 6-8 billion years ago
4. 10-15 billion years ago.

Answer: 2. 5-7 billion years ago

Question 22. Which one of the gases was absent at the time of the origin of life?

1. Oxygen
2. Methane
3. Hydrogen
4. Ammonia.

Answer: 1. Oxygen

Question 23. The theory of spontaneous generation of life explains that:

1. God created all life
2. Life originated de novo
3. Scientists created life in laboratories
4. Life begets life.

Answer: 2. Life originated de novo

Question 24. Cuvier suggested which of the following theories:

1. Mutation
2. Theory of special creation
3. Theory of catastrophism
4. Natural selection.

Answer: 3. Theory of catastrophism

Question 25. Who is regarded as the father of evolutionary concepts?

1. Linnaeus
2. Darwin
3. Lamarck
4. Empedocles.

Answer: 4. Empedocles.

Question 26. People who believed in the theory of “Spontaneous creation” assumed that:

1. Organisms arise only from other organisms
2. Organisms arise spontaneously
3. Organisms arise from water
4. Organisms arise spontaneously and also from similar organisms.

Answer: 2. Organisms arise spontaneously

Class 12 Biology MCQ Evolution Origin of Life  Question 27. The principle of sterilization is based upon experiments carried by:

1. I.A. Oparin
2. L.Pasteur
3. F. Redi
4. C. Spallanzani.

Answer: 2. L.Pasteur

Question 28. The idea that the egg of Eve or the sperm of Adam contained minute human was part of:

1. Theory of biogenesis
2. Concept of epigenesis
3. Theory of preformation
4. Theory of recapitulation.

Answer: 3. Theory of preformation

Question 29. The first organisms to appear on Earth were more like plants because:

1. Plants are similar
2. Plants are more
3. Plants do photosynthesis
4. None of these.

Answer: 3. Plants do photosynthesis

Question 30. Who of the following proved that life originated from simple amino acids:

1. Muller
2. Miller and Fisher
3. Oparin
4. de Vries.

Answer: 2. Miller and Fisher

Question 31. In Stanley Miller’s classic experiment:

1. Nucleic acids were formed
2. Ultraviolet radiation was used
3. Oxygen was one of the starting ingredients
4. Amino acids were formed.

Answer: 4. Amino acids were formed.

Question 32. Mitochondria contain particles made up of about 100 polypeptide molecules of several different types. The particles catalyze the production of acetyl Co A and carbon dioxide from pyruvate. When disassembled into the component polypeptides, no enzymatic activity is seen. These particles are examples of:

1. Spontaneous generation
2. Emergent properties of systems
3. The origin of life
4. Informational macromolecules.

Answer: 2. Emergent properties of systems

Question 33. Which of the following is not true of the microspheres studied by Sydney Fox?

1. They are formed by the addition of water to proteinoids
2. They are of uniform size, about 2μm in diameter.
3. Microspheres grow and bud off new microspheres
4. They are bounded by a layer of lipid
5. The boundary of a microsphere shows selective permeability.

Answer: 4. The boundary of a microsphere shows selective permeability.

Question 34. Coacervates maintained their entity with the help of

1. Lipid membrane
2. Protein membrane
3. Lipoprotein membrane
4. Glycoprotein membrane.

Answer: 1. Lipid membrane

Question 35. Nucleotides, porphyrins, polypeptides and other bio-chemicals developed non-enzymatically in early broth due to:

1. Oxygen free atmosphere
2. High temperature
3. Irradiated environment
4. All the above.

Answer: 4. All the above.

Question 36. Archaespheroides barbertonesis is:

1. Most primitive living prokaryote
2. Cambrian trilobite
3. Precambrian cyanobacterium
4. First eukaryote.

Answer: 3. Precambrian cyanobacterium

Class 12 Biology MCQ Evolution Origin of Life  Question 37. First eukaryotes evolved through:

1. Mutation in prokaryotes
2. Either mutation in prokaryotes or symbiotic association of different prokaryotes
3. Symbiotic association of different prokaryotes
4. None of the above.

Answer: 2. Either mutation in prokaryotes or symbiotic association of different prokaryotes

Question 38. The modem theory of the origin of life is related to:

1. A.I. Oparin
2. Cuvier
3. Epicurus
4. Lamarck.

Answer: 1. A.I. Oparin

Question 39. The primitive atmosphere of Earth was devoid of:

1. Ammonia
2. Free oxygen
3. Methane
4. Cyanamide.

Answer: 2. Free oxygen

Question 40. According to cosmozoic theory, life comes on Earth from other planets in space in the form of:

1. Spores
2. Seeds
3. Gametes
4. All the above.

Answer: 1. Spores

Question 41. The scientists related to the theory of spontaneous generation and experiments with swan-necked flasks are:

1. Van Helmont
2. Louis Pasteur
3. Miller
4. Haeckel.

Answer: 2. Louis Pasteur

Question 42. Under certain conditions scientists have obtained cell-like structures but not the true organisation of a cell. These are referred to as:

1. Microbes
2. Coacervates
3. Eobionts
4. Protists.

Answer: 2. Coacervates

Question 43. The theory of Pangenesis is related to:

1. Darwin
2. de Vries
3. Cuvier
4. Aristotle.

Answer: 1. Darwin

Question 44. Anaximander believed in the origin of life through:

1. Special creation
2. Spontaneous generation
3. Panspermia
4. Biogenesis.

Answer: 2. Spontaneous generation

Question 45. Spallanzani kept boiled nutrition broth indefinitely in:

1. Covered jars
2. Uncovered jars
3. Sealed flasks
4. Swan-necked flasks.

Answer: 3. Sealed flasks

Question 46. The term proto biogenesis is used for the theory of:

1. Special creation
2. Biochemical origin
3. Panspermia
4. Spontaneous generation.

Answer: 2. Biochemical origin

Origin and Evolution of Life MCQs Test Question 47. The correct sequence of origin of life is:

1. Coacervate, biomolecule, autotroph and heterotroph
2. Biomolecule, coacervate, autotroph and heterotroph
3. Coacervate, autotroph, biomolecule and heterotroph
4. None of the above.

Answer: 4. None of the above.

Question 48. One of the following appeared on the earth with the coming of the plants, and was absent in the past:

1. Carbon dioxide
2. Methane
3. Ammonia
4. Oxygen.

Answer: 4. Oxygen.

Question 49. Conditions of primitive earth were recreated in the laboratory and amino acids and bases were synthesized abiotically by:

1. Miller and Urey
2. Oparin A.I. and Haldane, J.B.S.
3. Oparin and Sydney fox
4. Louis Pasteur.

Answer: 1. Miller and Urey

Question 50. The theory that living organisms on the earth came from outer space is based on the study of:

1. Igneous
2. Sedimentary rocks
3. Meteorites
4. Moon soil.

Answer: 3. Meteorites

Question 51. Life cannot originate from inorganic materials at present because of:

1. High degree of environmental pollution
2. A very high amount of oxygen in the atmosphere
3. Very low atmospheric temperature
4. Absence of raw material.

Answer: 2. A very high amount of oxygen in the atmosphere

Origin and Evolution of Life MCQs Test Question 52. Choose the correct sequence during the formation of chemicals on early Earth:

1. Ammonia, water, nucleic acids and proteins
2. Ammonia, proteins, carbohydrates and nucleic acids
3. Ammonia, nucleic acids, proteins and carbohydrates
4. Proteins, carbohydrates, water and nucleic acids.

Answer: 2. Ammonia, proteins, carbohydrates and nucleic acids

Question 53. “Origin of Life was written by:

1. S.L. Miller
2. A.I. Oparin
3. De Vries
4. Charles Darwin.

Answer: 1. S.L. Miller

Question 54. Origin of life took place in/on:

1. Water
2. Air
3. Mountains
4. Land.

Answer: 2. Air

Question 55. Panspermia are:

1. Yeast
2. Life spores
3. Bacteria
4. Viruses.

Answer: 3. Bacteria

Question 56. Organic compounds first evolved on earth and required for the origin of life were:

1. Urea and amino acids
2. Proteins and nucleic acids
3. Proteins and amino acids
4. Urea and nucleic acids.

Answer: 2. Proteins and nucleic acids

Question 57. “All plants and animals were created and perpetrated themselves without any change”, is the theory of:

1. Genesis
2. Panspermia
3. Abiogenesis
4. Biogenesis.

Answer: 4. Biogenesis.

Origin and Evolution of Life MCQs Test Question 58. Origin of life occurred in:

1. Air
2. Soil
3. Mountains
4. Water.

Answer: 4. Water.

Question 59. The most important compounds for the origin of life were:

1. Nucleotides
2. Nucleic acids
3. Protein
4. Amino acids.

Answer: 1. Nucleotides

Question 60. Earth originated in the past:

1. 1.6 billion yrs.
2. 4.6 billion yrs.
3. 8.6 billion yrs.
4. 86 million yrs.

Answer: 3. 8.6 billion yrs.

NEET Biology Elements Of Heredity Multiple Choices Questions

Question 1. When one member of a pair of allelic genes expresses itself as a whole, it is a case of:

1. Dominance
2. Co-dominance
3. Incomplete dominance
4. None of these.

Answer: 1. Dominance

Question 2. The first generation of a given cross is known as :

1. F₂ generation
2. F₂ generation
3. F₁ generation
4. None of these.

Answer: 3. F₁ generation

Question 3. Gamete is:

1. Diploid sex cell
2. Haploid cell
3. Diploid somatic cell
4. Triploid somatic cell.

Answer: 2.Haploid cell

Read and Learn More NEET Biology Multiple Choice Question and Answers

Question 4. The genotype of the individual is :

1. Genetic constitution
2. Genetic setup
3. Both of these
4. None of these.

Answer: 3. Both of these

Principles of Inheritance And Variation NEET Questions Question 5. Fraternal twins air produced when :

1. Two ova are fertilized simultaneously
2. Single fertilised ovum  gets fertilised again
3. Two ova develop paitlicnogcnclically
4. Single ovum fertilized by two sperms.

Answer: 1. Two ova are fertilized simultaneously

Question 6. “Theory of pangenesis” to explain the mechanism of heredity was given by :

1. Mendel
2. Darwin
3. Lamarck
4. Cuvier.

Answer: 2. Darwin

Question 7. The I.Q. of a genius ranges from :

1. 70-80
2. 90-109
3. 110-139
4. 140 and more.

Answer: 1. 70-80

Question 8. The genetic setup is termed as :

1. Dominant
2. Genotype
3. Phenotype
4. Alleles.

Answer: 3. Phenotype

Question 9. It is the ratio of mental age to :

1. Chronological age × 100
2. Chronological age + 100
3. Chronological age — 100
4. Chronological age ÷ 100.

Answer: 1. Chronological age × 100

Principles of Inheritance And Variation NEET Questions Question 10. The sex of an unborn mammal can be predicted by :

1. Placental biopsy
2. Examining the chorion
3. Amniocentesis
4. Examine the mother’s blood.

Answer: 3. Amniocentesis

Question 11. Criminal syndrome :

1. XXY
2. XO
3. XYY
4. XY.

Answer: 3. XYY

Question 12. Gallon is associated with :

1. Eugenics
2. Euthenics
3. Genetics
4. Human genetics.

Answer: 1. Eugenics

Question 13. The term gene refers to :

1. The sequence of amino acid
2. A linkage group
3. A part of tRNA
4. A portion of DNA.

Answer: 4. A portion of DNA.

Question 14. Who connected cytology with genetics :

1. Morgan
2. Sutton
3. Bridges
4. Mendel.

Answer: 4. A portion of DNA.

Principles of Inheritance And Variation NEET Questions Question 15. The total of genes in a population is known as :

1. Gene bank
2. Gene linkage
3. Gene pool
4. Genome.

Answer: 3. Gene pool

Question 16. Which is the wholly genetic trail?

1. Diphtheria
2. Leucoderma
3. Albinism
4. Tuberculosis.

Answer: 3. Albinism

Question 17. The wife is a PTC non-taster and the husband is a PTC taster. Their son is a taster but daughters are non-tasters. This is not a sex-linked trait. Which pedigree is correct ?

Answer: 1

Question 18. Predict from the following chart 

1. Character is dominant and carried by X chromosome
2. Carried by Y chromosome
3. Character is sex-linked recessive
4. Character is recessive autosomal.

Answer: 3. Character is dominant and carried by X chromosome

Question 19. From the pedigree of a family given below, it is clear that the trait is inherited as a dominant autosomal trail. What will be the genotype of the mother and father?

1. Mother is aa and father is Aa
2. Father is AA and mother is aa
3. Father is Aa and mother is Aa
4. None of die above.

Answer: 1. Mother is aa and father is Aa

Question 20. When an individual possesses both alleles of its phenotypically dissimilar parent, it is called:

1. Homozygous
2. Mother is aa and father is Aa
3. Dioecious
4. Monoecious.

Answer: 2. Mother is aa and father is Aa

Question 21. In a pig dominant allele B produces black colour and its recessive allele b produces white. What would be the probable genotype of the offspring when a cross is made between individuals heterozygous for colour?

1. BB
2. Bb
3. bb
4. All of these.

Answer: 4. All of these.

Question 22. When the phenotype and genotypic ratio resemble the E, generation, it is an example of:

1. Incomplete dominance
2. Dihybrid cross
3. Cytoplasmic inheritance
4. Linkage.

Answer: 1. Incomplete dominance

Principles Of Inheritance And Variation MCQ NEET Question 23. Word heredity is derived from the Latin word ‘Hereditas’ which means :

1. Heirship
2. Ancestral property
3. Blood relations
4. All the above.

Answer: 1. Heirship

Question 24. Which of the following explains the law of dominance?

1. The expression of only one of the parental characters in a monohybrid cross in the F( generation
2. The expression of both in the F₂ generation
3. The proportion of 3:1 obtained in the F₂ generation
4. All of above

Answer: 4. All of the above

Question 25. Starch grain size in pea seed is an example of:

1. Incomplete dominance
2. Multiple alleles
3. Pleiotropism
4. Polygenic inheritance

Answer: 1. Incomplete dominance

Question 26. In family. father had traits but their mother did not. All that ‘one and daughter bail this hail The same hail wav lound in some granddaughters, though daughter married lo normal persons.

In this pedigree the genotypes of lather, mother and husbands of daughters am

1. The father is AA, the mother is aa, husband are aa
2. Father is AA, mother is aa, and husbands are AA
3. Father is aa, mother is Aa, husband Aa
4. Father is AA. mother AA, one husband Aa and second husband aa.

Answer: 4. Father is AA. mother AA, one husband Aa and second husband aa.

Principles Of Inheritance And Variation MCQ NEET Question 27. In sweet pea, genes C and P are necessary for colour in flowers. The flowers are white in the absence of either or both the genes. What will be the percentage of coloured flowers in the offspring of the cross Ccpp x ccPp?

1. 25%
2. 50%
3. 75%
4. 100%.

Answer: 1. 25%

Question 28. Polymorphism is mainly due to :

1. Monogenic inheritance
2. Polygenic inheritance
3. Both of the above
4. None of the above.

Answer: 3. Both of the above

Question 29. Continuous genetic variations are produced by :

1. Independent assortment
2. Mutations
3. Climatic changes
4. Interspecific hybridization.

Answer: 2. Mutations

Question 30. The alleles that produce independent effects in heterozygous conditions are called:

1. Supplementary alleles
2. Codominant alleles
3. Epistatic genes
4. Complementary alleles.

Answer: 1. Supplementary alleles

Question 31. In the following pedigree chart, the mutant trait is shaded black. The gene responsible for the trait is:

1. Dominant and sex-linked
2. Dominant but autosomal
3. Recessive and sex-linked
4. Recessive and autosomal.

Answer: 2. dominant but autosomal

Question 32. In the given pedigree, indicate whether the shaded symbols indicate a dominant or recessive allele.

1. Dominant
2. Recessive
3. Codominant
4. It can be recessive or dominant.

Answer: 3. recessive

Question 33. A dominant lethal gene Is that which

1. Allows nil organotin to survive and to tepfodiite
2. Allows an organism to sin vibe lull does not allow il to reproduce
3. Suppress the sex of the holder organism
4. Kills the organism in which it is present.

Answer: 4. Kills the organism in which it is present.

Biology MCQs with Answers Question 34. In humans, an example of a sex-linked trail is:

1. Sickle-cell anaemia
2. Curly hair
3. Down’s syndrome
4. Data are insufficient.

Answer: 1. Sickle-cell anaemia

Question 35. If the cell of an organism heterozygous for two pairs of genes represented by Aa,  undergoes meiosis, then the possible genotypic combination of gametes will be: 

1. AB, aB, Ah. ab
2. All, ab
3. Aa, Bb
4. Data are insufficient.

Answer: 3. Aa, Bb

Question 36. To determine whether variations of a character in a population were genetically controlled, the most appropriate procedure will be lo :

1. Measure the variations and see if they are continuous or discontinuous
2. Crossing individuals of both extremes and sec if the offspring and  parents show the same range of variations
3. Count the chromosomes and find out the variations in their number in the population
4. Examine the DNA of F| progeny in a cross between AA and aa.

Answer: 2. Crossing individuals of both extremes and sec if the offspring and parents show the same range of variations

Question 37. If Mendel had studied the 7 traits using a plant with 12 chromosomes instead of 14, in what way would his interpretation have been different?

1. He could have mapped the chromosome
2. He would have discovered blending or incomplete dominance
3. He would not have discovered the law of independent assortment
4. He would have discovered sex linkage.

Answer: 3. He would not have discovered the law of independent assortment

Biology MCQs with Answers Question 38. How many different types of genetically different gametes will be produced by a heterozygous plant having the genotype: AAB b Cc?

1. Nine
2. Two
3. Four
4. Six.

Answer: 3. Four

Question 39. Human skin colour is controlled by several gene pairs. Let us assume here that there are just three gene pairs on different chromosomes and that for each pair there are two alleles – an incompletely dominant one that codes for melanin deposition and an incompletely recessive one that codes for no melanin deposition. If a very dark-skinned person marries a very light-skinned woman, what will be the chance that their offspring will have very dark skin?

1. 0
2. 1/4
3. 5/8
4. 9/64
5. 3/64.

Answer: 1. 0

Question 40. The F₂ generation offspring in a plant showing incomplete dominance, exhibits’

1. Variable genotypic and phenotypic ratios
2. A genotypic ratio of 1: 1
3. A phenotypic ratio of 3:1
4. Similar phenotypic and genotypic ratios of 1: 2: 1.

Answer: 4. Similar phenotypic and genotypic ratios of 1: 2: 1.

Question 41. Two pea plants were subjected to cross-pollination. Of the 183 plants produced in the next generation, 94 plants were found to be tall and 89 plants were found to be dwarf. The genotypes of the two parental plants are likely to be :

1. TT and It
2. Tt and Tt
3. Tt and tt
4. TT and TT.

Answer: 3. Tt and tt

Question 42. Gametes are never hybrid? It is a statement of the law of:

1. Dominance
2. Segregation
3. Independent assortment
4. Random fertilization.

Answer: 2. Segregation

Biology MCQs with Answers Question 43. Which is correct about the traits chosen by Mendel?

1. The terminal pod is the dominant
2. The constricted pod is the dominant
3. Green coloured pod is the dominant
4. Tall plants are recessive.

Answer: 3. Green coloured pod is the dominant

Question 44. In a certain plant, red fruit (R) is dominant over yellow fruit (r) and tallness (T) is dominant over shortness (t). If a plant with an RRTt genotype is crossed with a plant rrtt genotype, what will be the percentage of tall plants with red fruits in the progeny?

1. 50%
2. 100%
3. 75%
4. 25%

Answer: 1. 50%

Question 45. Mendel obtained wrinkled seeds in pea due to the deposition of sugars instead of starch. It was due to which enzyme?

1. Amylase
2. Invertase
3. Dataset
4. Absence of starch branching

Answer: 4. Absence of starch branching

Question 46. The ratio of complementary genes is :

1. 9 : 3: 4
2. 12:3:1
3. 9 : 3 : 3: 4
4. 9:7

Answer: 4. 9:7

Question 47. When dominant and recessive allele express itself together, it is called :

1. Co-dominance
2. Dominance
3. Amphidominance
4. Pseudodominance.

Answer: 1. Co-dominance

Question 48. What is correct for blood group ‘O’?

1. No antigens but both a and b antibodies are present
2. An Antigen and b antibody
3. Antigen and antibody are both absent.
4. A and B antigens and a, b antibodies.

Answer: 1. No antigens but both a and b antibodies are present

Question 49. Sickle cell anaemia induces to:

1. Change of Amino Acid in α-chain of haemoglobin
2. Change of Amino Acid in β-chain of Haemoglobin
3. Change of Amino Acid in both a or β chain of Haemoglobin
4. Change of Amino Acid either a or β chain of Haemoglobin

Answer: 2. Change of Amino Acid in the β-chain of Haemoglobin

Question 50. Independent assortment of genes does not take place when :

1. Genes are located on homologous chromosomes
2. Genes are linked and located on the same chromosome
3. Genes are located on non-homologous chromosomes
4. All the above.

Answer: 2. Genes are linked and located on the same chromosome

NEET Biology Principles Of Inheritance And Variation

Genetics:(G.genesis_ descent) The study of the mechanism of inheritance and the control of the characteristics of an organism by its genes is called genetics. The name ‘genetics’ was first proposed by Bateson in 1906.

Heredity: (L he red inis = heirship). The transmission of characters, resemblances, and variations from one generation to another is called heredity.

Variations: The differences shown by the individuals of a species and also by the offspring of the same parents are referred to as variations.

Epigenetic Theory: A German zoologist, C.F. Wolff, proposed that neither the egg nor the sperm had a structure like a homunculus, but the gametes contained living substances capable of forming the embryo after fertilisation.

Magnetic power theory: Proposed by W. Harvey, it suggested that the utensils, through the friction of coitus, acquire some magnetic power to conceive an embryo. f-3 Kolreuter, the German botanist (1868), worked on crosses between different species of tobacco and gave some experimental evidence to prove that hereditary units tended to remain discrete in different generations.

Mendel: Mendel was the first to explain that heredity involved the transmission of units from the reproductive cells of the parents to the offspring.

NEET Biology Principles Of Inheritance And Variation Notes

Read and Learn More NEET Biology Notes

Hugo de Vries, Correns, and Tschermak rediscovered the laws of Mendel and extended the work by experiments on various plants and animals.

• The physical basis of heredity is genes, present on chromosomes, and the chemical basis of heredity is DNA.
• Various pre-Mendelian concepts such as Moist vapour theory, Fluid Theory (Empedocles), Reproductive Blood Theory by Aristotle, and Preformation Theory (Malpighi). Theory of Pangenesis- Maupertius, had been proposed

NEET Biology Principles Of Inheritance And Variation Mendelism

Gregor Johann Mendel is called the ‘Father of Genetics’ and the study of principles of heredity’ laid down by Mendel is called Mendelism.

• Mendel was born in 1822 and became a schoolteacher in 1854.
• Mendel studied physics, mathematics, and the natural sciences at Vienna University.
• Mendel procured 34 varieties of pea that showed clear differences in characteristics and used them in breeding experiments.

The seven traits (characters) which interested Mendel were:

1. Length of stem (plant height),
2. Shape of seed,
3. Seed colour ;
4. Pod colour,
5. Pod shape,
6. Flower colour
7. Flower position.

Mendel studied the law of heredity. Mendel simply described the results of his crosses based on meiosis and fertilization and drew certain conclusions. Correns gave these conclusions the shape of laws.

• But his laws were rediscovered and finally got recognition in 1900 through the discoveries of Hugo de Vries, Carl Correns, and E.V. Tschermak.
• Mendel presented his “Experiments in Plant Hybridization” before the Brunn Natural Society on February 8, 1865. The society published Mendel’s research in 1866.

Mendel’s Law Of Dominance. This law states that the character that expresses itself in the F₁ generation is dominant, and the alternative character not expressed is recessive. The law of purity of gametes, also called the law of splitting of hybrids, states that each gamete receives only one gene of a trait.

Menders laws Of segregation: According to this law, the factors regulating character are separated during the formation, and hence only one of the pairs is transmitted by a particular gamete.

Mendel Law Of Independent Assortment: This law states that when there are two or more pairs of factors. The members of one of the factors segregate and assort independently of other pairs.

NEET Biology Principles Of Inheritance And Variation Notes

NEET Biology Principles Of Inheritance And Variation Terminology Used In Genetics

Gene: According to Mendel, a gene (factor or determinant) is a unit all is ivs|vnsiMe tor die transmission and expression of a hereditary trait. A gene has two different forms or alleles.”
Or
The concept of the gene resulted from a convergence of cytology and genetics is gene is a segment of chromosomes which acts as a carrier of characters.
Or
Gene is a segment of nucleic acid that is responsible for the transmission and expression of a hereditary trail. A gone may have a large number of hereditary alleles that arise by mutation or by recombination.
Or
Gene is a segment of DNA which expresses itself by directing the synthesis of specific polypeptides.

• The term gene was given by Johannsen (in 1909). A gene is a unit of inheritance which is carried from a parent by a gamete in a chromosome and controls the expression of a specific character in the young one.
• Genotype: It refers to the genetic makeup of an organism (Johannsen 1909). Genotype is the gene complement or genetic constituent of an individual about one or more characters irrespective of whether genes are expressed or not.

Phenotype: (Johannsen, 1911) It is a measurable or observable distinctive structural and functional characteristic of an individual about one or more characters which is a result of gene products brought to expression in a given environment.

• The characteristic may be visible to the eyes Example (the height of a plant) or may require speculation for its identification (for example., a serological test for a blood group.)
• The tall pea plants have two types of genetic combinations (TT and Tt). Irrespective of the genetic set up they develop the same character. Thus phenotype is dependent upon genotype and expressibility of its genes.

Alleles or Allelomorphs: (Allele-belonging to one another). It is used to refer to one member of a gene pair.

• According to Mendel, two genes representing two alternatives of a character are present on two separate chromosomes of a homologous pair but at the corresponding loci Example in the gene pair, A (tall) is present on one chromosome and (dwarf) is on the other chromosome.
• Each of them is called an allele, i.e. T. an allele to T and vice versa.
• Pseudoalleles: Genes having separate but nearby loci and controlling the same trait In Drosophila, the genes for apricot and white eye colour are pseudoalleles. Duplicate Genes.
• Two pairs of genes lie in different chromosomes and produce a single trait with or without a cumulative effect. The coat colour in the Duroc-jersey breed of pigs depends on 2 pairs of genes.

Lethal Genes: Genes that make the organism having them inviable to live. In the yellow race of mouse, Mus musculus, the genes YY kill the embryos.

Atavism (Reversion). Occasional reappearance of a remote ancestral trait in some individuals. Example A short tail in some babies.

Dominant Factor: A heterozygote possesses two contrasting genes but only one of the two can express itself while the other remains hidden.

• The gene which gains expression in the F₁ hybrid is known as the dominant Example (T is dominant and masks the t).
• Recessive factor: The factor of an allelomorphic pair which is unable to express itself in the presence of its contracting factor is called the recessive factor in the case of Tt.
• Wild type: The commonly occurring phenotype in the natural breeding population is called wild type.

Hoinozvgotc: It is the individual whose homologous chromosomes bear identical genes or alleles of a given allelic pair and produces gametes all example RR.rr, TT. u.TTRR etc.

Heterozygote: It is the individual whose homologous chromosomes bear unidentical or dissimilar genes or alleles of a given allelic pair and produces dissimilar or different types of gametes, for example, Tt, Rr, Tt Yy etc. (The number of the types of gametes produced by heterozygote can be found out by the formula 2n where ‘n’ stands for the number of pairs of contrasting characters present in the heterozygote). It is also called hybrid.

NEET Biology Principles Of Inheritance And Variation Notes

• Hybrid vigour or Heterosis: It is the increased vigour or strength of the hybrids than their parents. It is of superior quality to either of the parents.
• Pure Line (Johannsen, 1900). The series of generations of organisms or descendants which breed true because they are derived from a single self-fertilized homozygous ancestor or identical homozygous ancestors (members of a pure line are therefore homozygous for one or more characters).
• Linkage: Linkage was first seen by Sutton. Term linkage was given by Morgan. It is the phenomenon of staying together of certain genes during inheritance through several generations without any change or separation.
• Back Cross: It is a cross which is performed between a hybrid and one of its parents. In plant breeding, a back cross is performed a few times to increase the traits of that parent.

Test Cross: It is a cross to know whether an individual is homozygous or heterozygous for a dominant character. The individual is crossed with a recessive parent.

• The offspring will be 100% dominant if an individual is homozygous dominant. The ratio will be 50% dominant and 50% recessive in the case of hybrid or heterozygous individuals.
• Thus monohybrid test cross ratio is 1:1 In case of double heterozygote (Rr Yy) crossed with double recessive (rryy) the ratio will be 1:1:1:1.

Out Cross: Cross between F₁ individuals and homozygous dominant parent to improve or produce hybrid plants which are superior to parents, we make out-cross.

• Eugenics: The application of genetics in an attempt to improve the hereditary qualities of humans.
• Gene locus: Location of a particular gene (or one of its alleles) on a chromosome.
• Polyploidy: Having three or more complete sets of chromosomes.
• Qualitative inheritance: It is a type of inheritance in which a single gene influences a complement.

Principles Of Inheritance And Variation NEET Notes

Penetrance: A genotype can produce its phenotype in an individual. It is of 2 types :

1. Complete Penetrance Full expression of a genotype in an individual. In humans, the allele B for brown eyes and the allele b for blue eyes have complete penetrance in the homozygous condition, BB, bb. The allele B has complete penetrance even in the heterozygous condition, Bb also.
2. Incomplete (Reduced) Penetrance. Failure of a genotype to express in all cases. In humans, diabetes Mellitus is genetically controlled. However, not all persons carrying the genes for this disorder develop it.

Relation among pairs of independent alleles Gametes F₂ genotypes and F₂ phenotypes when domainer is prevented:

Self Stecrility: Hound in plants having multiple alleles for compatibility incompatibility reaction – S₁, S₂, S₃, S₄, S₅, S₆, etc. A plant carries two such allelesExample S₁, S₂, S₂, S₃, S₁, S₃,S₂,S_4,S_3,S₅.

• A pollen grain carries only one allele. If it happens to be one of the two alleles of the pistil, the pollen grain fails to form a pollen tube.
• Heterodominance or Overdominance or Superdominance: Scrra( 1959) described when F₁ generation heterozygotes have a more complex phenotype than that of a corresponding parent, it is termed hetero-dominance.

F₁ Generation: The F₁ or First filial (Filus — son and filial—daughter) generation is the generation of hybrids produced from a cross between two genetically different individuals called parents as Tt individuals are produced from a cross between TT and tt parent.

F₂Generation. F₂ or Second filial generation is the generation of individuals which arises as a result of inter-breeding amongst individuals of the F₁ generation.

• Principle of Paired Factors. Each character is represented in an individual by two determinants, factors or genes. They are similar in homozygous individuals which breed true. The factor or a character represents two alternatives of a trait in hybrids.
• Monohybrid Cross: It involves the study of the inheritance of one pair of contrasting characters.
• Monohybrid Ratio: It is the ratio obtained in the F₂ generation when a monohybrid cross is made and the offspring of the F₁ generation are self-bred. Monohybrid ratio is usually 3 :1 (phenotypically) and 1: 2 :1 (genotypically).
• Dihvbrid Cross: It is a cross between two organisms of a species which is made to study the inheritance of two pairs of characters.

Trihybrid Cross: A cross between homozygous parents that differ in three gene pairs (i.e. producing trihybrids) is a combination of three single-pair crosses operating together. Thus (AA x aa), (BB x bb) and (CC x cc) could be combined in the same cross.

Principles Of Inheritance And Variation NEET Notes

• Dihybrid Ratio: It is the ratio obtained in the F9 generation when a dihybrid cross is made and the offspring of the F₁ generation are self-bred. Phenotypically it is 9:3:3:1.
• Trihybrid ratio: Ratio in F₂ obtained in a trihybrid cross represented by a Punnet square. 64 (8n) squares would be required with a phenotypic ratio of 27:9:9:9: 3:3:3:1.
• Polyhybrid Cross: It includes those characters in which inheritance of more than two pairs of genes are considered.
• Reciprocal Crosses: These crosses involve two concerning the same characters but with reversed sexes. It means if in a first cross, A is used as the female parent and B as the male parent, then in 2nd or reciprocal crosses A will be used as the male parent and B as the female parent.

Punnet Square: It is a chequerboard used to show the results of a cross between two organisms. The chequerboard was devised by R.C. Punnet. It depicts both the genotype and phenotype of the progeny.

• Dihybrid: An individual that is heterozygous for two pairs of alleles. The progeny of a cross between homozygous parents differs in two respects.
• Homozygous: The condition in which only one allele of a pair is present, as in sex linkage or as a result of deletion.

The formula for number of genotypes in case of multiple alleles is \(\frac{n}{2}(n+1)\) = n Alleles. i.e. in the case of the blood group system, 3 alleles regulate the ABO blood group thus number of the genotype formed will be six.

• If a cross is made between two yeasts having genotype Aa Bb Cc. then the probability of getting genotype aa bb cc will be 1/64 because if we consider individuals the probabilities of occurring of aa, bb and cc is — \(\frac{1}{4}\) therefore = \(\frac{1}{(4)^3}=\frac{1}{64}\)
• Three genotypes are produced by two alleles.
• Even Aa Bb Cc DD Ee Ff produces 32 different gametes.
• A recessive allele in the zygote appears only if both parents possess this allele.
• Progeny = offspring ir
• Siblings or sibs, Individuals having the same parents, brothers and sisters.

Principles Of Inheritance And Variation NEET Notes

NEET Biology Principles Of Inheritance And Variation Modifications Of Mendelian Ratio And Gene Interaction

Gene interaction. It is the influence of one gene (allele) over another which causes a change in expression, and phenotype of normal Mendelian ratios like 3: 1 (monohybrid cross) and9:3:3:l(dihybrid cross.).It may be intragenic (intr alleles) or intergallic (non-allelic). They are of the following types :

• ID Incompletedominance (Intermediateinheritance). It is the phenomenon where none of the two Mendelian factors, alleles or genes is dominant over the other.
• Genotypic and phenotypic ratios are the same in the F2 generation i.e. 1:2:1. Example. Illustrated in Mirabilis jalapa (Four o’clock), Antirrhinum (Snapdragon or Dog flower) and Andalusian fowls.
• In a dihybrid cross if one trait follows the law of dominance the other shows incomplete dominance, the ratio comes to be 3: 6: 3:1 : 2: 1 and if both traits show incomplete dominance, it will be1: 2:1: 2: 4: 2: 1.
• Codominance. It is the equal and independent expression of two alleles of a trait when they are present together in an individual. The phenotype of a heterozygous individual is different from either of the homozygous.
• Example. A, B, AB and O blood group.

NEET Principles Of Inheritance And Variation Chapter Notes

Duplicate Genes (15: 1) Observed by G.H. Shell Pseudoalleles or Duplicate genes or factors are two or more independent genes present on different chromosomes which determine the same or nearly the same phenotype in a dominant state so that either of them can produce the same character. The independent genes do not have a polymetric effect, e.g. Endosperm colour in maize, fruit shape in Shepherd’s’ purse, and inheritance of grain colour in Avena sativa (Oat).

• Polymetric or Additive genes (9:6: 1). They are duplicate genes with cumulative effects. Two independent dominant genes, whether present in homozygous or heterozygous conditions have similar phenotypic effects when present individually but produce a cumulative or double effect when found together for example Summer squash plant (Cucurbita pepo) has three types of fruit forms.

Polygenes (Quantitative inheritance) or Multiple genes or Cumulative genes. There are many characteristics in both plants and animals which are controlled by the cumulative action of dominant alleles of generally two or more independent genes for example., height, weight, size of fruits, number of grains in an ear, skin colour in mah.

NEET Principles Of Inheritance And Variation Chapter Notes

Illustrations of Polygenes in Human Skin Colour

• Human skin colour is controlled by the polygenic effect of at least three separate genes.
• Each gene contributes to a unit of darkness’ due to incomplete dominance. ‘
• Skin colour is determined by cumulative genes and this hypothesis was designed by Davenport and Davenport in 1910.
• Davenport and Davenport designated five phenotypic classes controlled by genes A . and B (like kernel colour of wheat)

Hughes (1944) recognized seven phenotypic classes designating genes A, B and C.

• The skin shades vary from very dark in AABBCC individuals to very light in an aabbcc individual.
• A person with AaBbCc (i.e. heterozygous for all three genes) will have an intermediate colour termed mulatto.
• The number of possible allele combinations in the gametes is eight (ABC, ABc, AbC, aBC, abC, aBC, abe. abc) for such a person.
• So a total of 64 phenotypic combinations is possible when two persons of ABC x abc gene combinations marry.

NEET Principles Of Inheritance And Variation Chapter Notes

NEET Biology Principles Of Inheritance And Variation Characteristics Of Polygene

1. Negligible effect of environment.
2. No involvement of linkage and epistasis.
3. The quality of the gene does not matter.
4. Each contributing gene (allele) in a series produces an equal effect.
5. The effect of each contributing gene is additive (cumulative).

Short Cut Method To Predict The Phenotype Ratio Of Polygenic Inheritance :

• We should know the numbers of total alleles involved in a quantitative inheritance to predict the phenotype ratio of F-, generation.
• This prediction can be shov/n with the help of Pascal’s triangle: e.g. Kernel colour of wheat there are 4 alleles and a ratio of 1: 4 : 6: 4: 1 is obtained.
• Nilsson-Eble (1908) obtained the first experimental proof of polygenic inheritance.

Principles Of Inheritance And Variation Class 12 Notes For NEET

Some Ratios Of Polygenic Inheritance:

Quantitative or polygenic inheritance was first studied by J. Kolreuter in the case of tobacco and F. Galton in the case of human beings, Nilsson-Ehle in kernel colour in wheat and Emerson and East studied it in cob length in maize. Davenport studied skin colour in man

The relative contribution of each polygene

= \(\frac{\text { Maximum height }- \text { minimum average height }}{\text { Total number of polygenes }}\)

• Complementary genes (9:7) (Bateson and Punnet 1906). These non-allelic genes independently show a similar effect but produce a new (rail when present together in dominant form for example., flower colour in sweet pea, grain colour In lice, grain colour in Sorghum.
• Supplementary genes (9:3: 4): They are a pair of non-allelic genes; one of which produces its effect independently when in the dominant state while the dominant allele of the other is without any independent effect but can produce a new trait along with the dominant allele of the form example Glume colour in Sorghum emulation, Seed colour in Lab lab, Coat colour in mice and guinea pig.
• Collaboration: Epistasis of complementary and supplementary genes produces a ratio of 27: 37. c.g. Maize colour pigment anthocyanin is due to two complementary genes and one supplementary gene.

Principles Of Inheritance And Variation Class 12 Notes For NEET

Epistasis: It is the phenomenon of masking or suppressing the expression of a nonallelic gene. The gene which suppresses other non-allelic genes is called the epistatic gene while the gene or locus which is suppressed by the non-allelic gene is called the hypostatic gene.

• Dominant epistasis (12: 3:1): The dominant allele at one locus suppresses the expression of another gene regardless of its allelic condition ( dominant or recessive)Example Fruit colour in cucurbita (yellow, green and white), coat colour in the dog (White, black and brown).
• Recessive epistasis (9:3:4): In this case, recessive homozygous genotype at one locus (aa) suppresses the expression of non-alleles at another locus. The latter can produce their effect only when a dominant allele occurs at the first example Pigmentation in onion bulb, and coat colour in mice.
• Dominant-recessive epistasis (13 : 3): Here the dominant allele at one locus (A-) and recessive allele at another locus (bb) give rise to the same effect. (A-B, A-bb, aabb) other gene combinations produce different phenotypesExample Plumage colour in poultry birds.

Summary Of Epistatic Ratios:

Lethal genes. These genes kill the organism when they can express their effect. Dominant or homozygous recessive, for Example, Sickle cell anaemia, Fur colour in mice (first studied by Cuenot in 1905)

Principles Of Inheritance And Variation Class 12 Notes For NEET

• E. Baur. Observed lethal genes in. Snapdragon (Antirrhinum) ill Yellow Lethals in Mice
• Lucien Cuenot (1905) reported an incompletely dominant allele Y for yellow coats in mice.
• ‘A’ represents a gene for yellow and ‘n’ one for black.
• W. Castle and C. Little (1910) proposed that the yellow homozygotes were aborted in the uterus.
• In other words, the yellow allele has a dominant effect on coat colour but acts as a recessive allele concerning the lethality phenotype.

Albinism In Corn (Zea mays)

• Albinism in corn is due to a lethal gene.
• The gene ‘G’ is for normal chlorophyll production. It is completely dominant to its allele.
• G plants contain chlorophyll and are photosynthetic.
• On the other hand, gg plants produce no chlorophyll and are yellowish white and die.

Pleiotropic Genes: These genes have multiple effects because they influence several traits simultaneously.

Examples

1. Marphan’s syndrome is caused in human beings by a pleiotropic gene which is characterised by a slender body, limb elongation, hypermobility in joints, lens dislocation and a tendency to develop heart diseases.
2. Sickle cell anaemia. Sickle cell anaemia disease is caused by gene (Hbs) which is lethal in the homozygous condition but has a slightly detectable effect in the heterozygous condition. In sickle cell anaemia, a change in the shape of red blood cells occurs in the venous blood.

Being deficient in oxygen tension, these erythrocytes show a marked change in their structure attaining a sickle-shaped structure. As a result, rupturing of cells may take place and chronic haemolytic anaemia is caused.

• This disease is caused when the gene responsible for haemoglobin produced by recessive alleles differs in one amino acid i.e. it incorporates valine in place of glutamic acid, at the 6th position of the β-chain.
• Sickle cell anaemia is common in persons of African descent and is also found in some other parts of the world where malaria is, or has been major cause of death.
• In heterozygotes Hb^AHb^S, some red cells contain haemoglobin A, and other haemoglobin S. Because both types of haemoglobin, rather than a single intermediate form are produced, it is also a case of codominance.
• Under normal conditions, heterozygotes manifest none of the severe symptoms of HbsHbs persons, though they may suffer some periodic discomfort and even develop anaemia after a time at high altitude.

Principles Of Inheritance And Variation Class 12 Notes For NEET

Explanations for various genotypes are :

• Hb^AHb^S — Normal (Haemoglobin A only: no sickling)
• Hb^AHb^S — Sickle cell trait (Haemoglobin A and S: sickling under reduced oxygen tension)
• Hb^SHb^S — Sickle cell anaemia (Haemoglobin S only: sickling under normal oxygen tension)

Sickle cell anaemia can also be considered a case of lethal genes.

• A lethal gene can be defined as a gene whose phenotypic effect is sufficiently drastic to kill the bearer.
• The expected ratio in lethal gene cases comes equal to 2: 1.
• In sickle cell anaemia, death is caused by Hb^SHb^S condition.

Multiple Alleles:

Genes possessing multiple alternative forms, such as 15 alleles for eye color in Drosophila.

• Four alleles determine coat colour in rabbits. ABO blood groupings.
• Multiple alleles exhibit the following characteristics
• Several alleles are situated at the identical locus on the chromosome.
• Several alleles govern a specific trait.
• Crossover events do not occur across multiple alleles since they occupy the same locus.
• Multiple alleles can exhibit dominant or intermediate traits, but the wild type in the series is often dominant.
• Wild type or dominant alleles are denoted by uppercase letters, whereas recessive alleles are indicated by lowercase letters

Blond groups:

Viv determined by two types of antigens (A and B) present on the surtax coating to R.B.C.These antigens occur in the oligosaccharides-rich head regions of a glycophorin.

NEET Biology Principles Of Inheritance And Variation Revision Notes

Showing phenotype, genotype and antigen.

• Additive Factors: Polygenes affecting the same trait, with each enhancing the phenotype.
• Concordance: Identity of matched pairs or groups for a given trait; for example, identical twins both expressing the same genetic syndrome.

NEET Biology Principles Of Inheritance And Variation Revision Notes

NEET Biology Principles Of Inheritance And Variation Important Contributors

E. Haeckel:

Inheritance transmission via the nucleus.

• Pythagoras: He posited the hypothesis of moist vapour.
  Empedocles proposed that each bodily portion generated a fluid, so introducing the fluid theory of inheritance.
• Aristotle proposed the hypothesis of reproductive blood.
• Darwin posited that each somatic cell and tissue in the body generates minute particles known as gemmules or pangene, which encapsulate both hereditary and acquired traits.
• Leeuwenhoek: First observed spermatozoa.
• Malpighi posited that a homunculus, or miniature individual, exists within sperm or egg cells.
• Maupertuis proposed the notion of pangenesis, positing that heredity is governed by minute particles.
• Kolreuter, a German botanist. He produced viable interspecific hybrids in tobacco. He is the ‘‘father of polygenic inheritance.”

Gregor Johann Mendel. Father of genetics as he was the first to demonstrate the mechanism of transmission of characteristics and biochemical disorders of man.

• Johannsen. Coined the terms gene and genotype, phenotype and pure line.
• Gallon. Started pedigree analysis.
• R.C. Funnel. Used a chequerboard called Punnet square to show the results of a cross between two organisms.
• Sir Archibald Garrod. Studied ABO blood types.
• F. Gallon. He studied polygenic inheritance in man and coined the term eugenics.
• Nilsson-Ehlc. Obtained the first experimental proof of polygenic inheritance in the case of kernel colour of wheat.
• Karl Landsteiner. (1907) discovered A. B, O blood groups.
• Gastello and Steini (1902) discovered the A B blood group.
• Kolreuter: (German botanist). He obtained fertile interspecific hybrids in tobacco. He is the “father of polygenic inheritance.
• Karl Landsteiner and Weiner discovered the Rh Factor.
• Corrrens, de Vries and Tsechermak rediscovered Mendel’s theory ol inheritance. Also discovered incomplete dominance and cytoplasmic inheritance.

NEET Biology Principles Of Inheritance And Variation Revision Notes

NEET Biology Principles Of Inheritance And Variation Some Important Ratios

NEET Biology Principles Of Inheritance And Variation Revision Notes

NEET Biology Principles Of Inheritance And Variation Variations

All living beings exhibit variations in practically every character and almost all directions.

• The differences shown by the individuals of a species also by the offspring of the same parents are referred to as variations.
• All organisms change themselves to adapt themselves to the changing environment, otherwise they fail to survive. Variations are classified in two ways i.e.

As per the nature of the cells, it affects.

Somatic variations. Such variations are not inherited from parents and affect the omalic cells only.

• They are acquired by an organism during its lifetime and are lost with death Hence, such variations are also called acquired variations. There are possible causes for such variations :

Three possible causes of acquired variations are :

1. Environmental Factors i.e. medium, light, temperature, nutrition and water.
2. Use of disuse of organs
3. Conscious efforts

Germinal variations (Blastogenic Variations). These variations cause the line to grow cells and are thus inheritable for haemophilia, blood groups, colour-blindness, hairiness, eve vvIihii etc SikIi satiations may be due to the following reasons. As per the degree of difference produced. 2 types

1. Merstic = Influence the mnnlicr of parts
2. Substantive = Inllncnec the shape, size, weight and colour.

Continuous sanctions: Variation not represented by distinct classes. Individuals grade into each other and measurement data are required for analysis (cf. Discontinuous variation), Multiple genes or polygenes are usually responsible for Ibis type of variation, (or Fluctuating variations).

• Discontinuous variations. Distinct classes such as red versus white, tall versus dwarf (rf. Continuous variation).
• Transgressive variation. The appearance in (lie F₂ (or later) generation of individuals, showing n more extreme development of a trait than shown in either original parent. It is due to polygenic inheritance discovered by Punnet and Hailey.
• Determinate Variations (Orthogenic variation). Adaptive and selective variations of definite evolutionary lines, developing progressively generation after generation.
• Indeterminate variations. Variations occurring in any conceivable direction and are not governed by any law may give a distinct advantage to the possessor in its light for existence.

Techniques Used To Study Lutinuii Genetics

1. Pedigree analysis
2. Population genetics
3. Human karyotype.

Pedigree analysis: Pedigree is a record of the inheritance of certain traits for two or more generations presented in the form of a diagram family tree or symbols. Different symbols used are.

• The idea dial disorders are inherited has been prevailing in human society for a long. Dus was based on the heritability of certain characteristic features in families.
• After the rediscovery of Mendel’s work, the practice of analysing the inheritance patterns of traits in human living began.
• Since it is evident that control crosses that can be performed in plants or some other organisms, are not possible in the case of human beings, the study of the family history about inheritance of a particular trail provides an alternative.
• Such an analysis of traits in several of generations of a family is called the pedigree analysis. In the pedigree analysis, the inheritance of a particular trait is represented in the family tree over generations.
• In human genetics, pedigree study provides a strong tool, which is utilised to trace die inheritance of a specific trait, abnormality or disease.

Population genetics:

• It is the study of the distribution of units and the frequency of genes within the total population.
• The formula delineating the genotypic expectations of progeny in relation to the gametic (allelic) frequencies of the gene pool was proposed by Hardy and Weinberg and is referred to as the Hardy-Weinberg principle.

Principles Of Inheritance And Variation NEET Chapter Summary

This law is applicable only if:

1. Populationis is large and pamniclie (Random matiing).
2. No selecting, no imitation.
3. Population is closed.

under these conditions, according to Hardy and Weinberg’s Law. there.should be no change in the gametic or zygotic frequencies from generation to generation.

Expected genotype pic (zygotic) frequencies in generations may be summarised as

⇒ (p+q)²=P²+2pq+q²=1.0

⇒ P² = frequency of dominant gene/alleles.

⇒ q² = frequency of recessive gene/alleles P=k=1

⇒ p² + 2pq = frequency of dominant trait.

⇒ q² = frequency of a recessive trait.

Human Karyotype: Tjio and Levan first prepared a human karyotype.

• It is an arrangement of chromosomes according to the length of chromosomes and the position of the centromere.
• A pencil sketch or photograph of a karyotype is called an idiogram.
• It is an asymmetrical karyotype which is considered an advanced character.

Principles Of Inheritance And Variation NEET Chapter Summary

Classification of chromosomes: The human metaphase chromosomes were First of all classified in a conference of cytogeneticists at Denver, Colorado in I960.

• In humans 23 pairs (46) chromosomes have been numbered from l to 23 according to their decreasing size, Patau (I960) divided the human chromosome into the following seven groups designated A to G.

• Banding Technique: It is the development of risk ami light band of stains on the chlorosome when they are treated with special fluorescent lives.
• Hits are because different parts of the chromosome show differential affinity to these stains.
• Chromosome handling was discovered by Caspersson et al (1970) and Paridue and Galt(1970) almost simultaneously late as different types of stains and staining techniques.
• Each develops a unique banding pattern which remains constant.

Principles Of Inheritance And Variation NEET Chapter Summary

• Continuity of life is made possible by asexual and sexual reproduction Sexual reproduction, besides creating new individuals introduces variability in the offspring by combining trials of parents.
• The genotypic ratio of the dihybrid cross is RRYY: RrYY : RRYy: rrYY: RrYy : rrYy: ItRyy : Rryy: rryy 1:2: 2:1:4:2:1:2:1
• In the case of MN blood groups in humans, alleles show codominance. The red blood cells can carry two types of native antigens, M and N, and an individual can be MM, MN or NN exhibiting either one or both of them
• ABO blood group system shows codominance, multiple alleles and dominant recessive gene interaction.
• Treatment with gibberellic acid only brings phenotypic changes and genes are not affected.
• Pleiotropy results in different expressions at the phenotypic level. For example, sickle cell anaemia and cystic fibrosis in men.
• Morgan is called the father of experimental genetics. Bateson is called the father of modern genetics. Nilsson-Ehle (1908) was the first scientist to prove quantitative inheritance.
• At the time of fertilization, the chance factor is responsible for the fusion of gametes. Infinite new combinations are produced Example 70 × 10¹² for 23 pairs of chromosomes.

Cause Of Variations Is Hidden In Sexual Reproduction

Mendel’s Laws of Inheritance:

1. Law of paired factors
2. Law or Principle of Dominance Law of Segregation.
3. Phenotypic ratio = 3:1 Monohybrid genotypic ratio =1:2:1
4. Law of Independent assortment Dihybrid phenotypic ratio = 9 : 3 : 3: 1 Dihybrid  genotypic ratio = 1: 2 : 1: 2 : 4: 2 : 1: 2: 1

Exceptions To Mendelism

• Incomplete Dominance = Genotypic and phenotypic ratio =1:2:1
• Codominance. I^AI^A (In the case of blood groups)
• Hb^AHb^A (In case of sickle cell anaemia)
• Multiple alleles. 15 alleles for eye colour in Drosophila, 3 alleles for blood groups in humans (I^A, I^A and 1° for four types of blood groups (A, B, AB and O.)
• Chromosomal theory of inheritance proposed by Sutton and Boveri (1902)
• Experimental verification by Morgan with his experiments on Drosophila melanogaster.
• Linkage. Physical association of two genes on a chromosome.
• Recombination. Generation of non-parental gene combination.
• Sex Determination.

Principles Of Inheritance And Variation NEET Chapter Summary

Human : Autosomes + XY → Male, Autosomes + XX → Female

Most of the insects (Male heterogamy).

• Grasshopper AA + XO → Male
• AA + XX → Female
• Birds AA + ZW → Female
• AA + ZZ → Male

Mutation

1. Chromosomal mutation
2. Point mutation — Sickle cell anaemia
3. Frameshift mutation.

Mutagen—Physical agents which cause mutation: UV radiation and Chemical Mutagen.

Pedigree Analysis Male and Female Analysis of Traits.Marriage between close relatives 0=0

NEET Biology Principles Of Inheritance And Variation Study Material

NEET Biology Principles Of Inheritance And Variation Elements Of Heredity And Variations Conclusion

In sickle cell anemia, glutamic acid is substituted by valine at the sixth position in the β-chain of haemoglobin.

• In thalassemia, a genetic blood condition characterized by anemia, the β-chain of haemoglobin is altered due to a frameshift mutation. Bone marrow is absent.
• Either the mother must be Rh positive, or both the mother and the husband must be Rh negative; otherwise, the second kid may suffer erythroblastosis fetalis.
• Rh positive is genetically prevalent in humans.
• The back cross is a genetic cross formulated by Mendel in which the F1 generation is mated with an individual possessing the same genotype as one of the parental organisms.
• The colouration of sweet pea flowers is attributed to a substance known as anthocyanin. It is released by a sequence of metabolic processes involving distinct enzymes.

The formation of each enzyme is determined by separate genes the mutant white tigers now seen in Indian zoos, a defective pleiotropic gene influences both fur colouration and the connection between the eye and brain during development.

• The trihybrid ratio shows the same pattern of inheritance as the dihybrid. The phenotype ratio will be 27: 9 : 9: 9 : 3 : 3 : 3: 1.
• When the heterozygotes have a more extreme phenotype than either of the corresponding homozygotes, then it is usually called over-dominance, super-dominance and hetero-dominance.
• Parasexual hybridisation. It is defined as the technique of hybridisation through protoplast fission. The protoplast fusion opens up the possibility of overcoming the sexual barriers and of mixing and reassorting the genetic element of sexually isolated organisms

• Mendel used the word unit factor or pair factors for controlling units by various traits because he was unaware of the word gene.
• Epistasis is a Greek word which means the act of stopping or inhibiting.
• Non-allelic genes are those present in different loci.
• Genealogy: The history of descent of a person or its family is termed genealogy.
• Modifier Genes: Genes that alter or modify the expression of other non-allelic genes. Modifier genes produce a variety of crests on pigeons’ heads.

NEET Biology Enzymes

Enzymes. serval definitions given for enzymes are as follows:

• The catalyst in living cells facilitates metabolic reactions.
• The enzymes arc directing and controlling catalysts that determine the particular chemical reaction which makes up the complex metabolic pattern of living organisms.
• A protein with catalytic properties due to its power of specific activation.
• Enzymes are organic catalysts.

Enzymes are proteinic substances that act as biological catalysts with a high degree of specificity produced within the cell having an enormous ability to catalyze all metabolic reactions in a highly effective manner. Enzymes may be simple proteins or conjugated proteins formed of apoenzyme (protein part) and cofactor (prosthetic group or coenzymes or metallic cofactor). Å

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Enzymes NEET Notes

Discovery of enzyme

• Edward Buchner (1897) showed that the juice of groundnut and preserved yeast cells ferment sugar.
• The Tenn enzyme was coined by VV. Kuhne.
• J.B. Sumner purified and crystallized urease enzymes from Jack beans. He also suggested that enzymes are proteins.

Properties

• Enzymes function as catalysts, necessitate minimal quantities, exhibit great specificity, and perform optimally at temperatures ranging from 25 to 40°C; low temperatures impede activity, while elevated temperatures lead to denaturation.
• Enzymes necessitate an optimal pH tailored to each individual enzyme. The ratio of enzyme to substrate concentration influences the reaction rate.
• Certain inhibitors impede enzymatic activity. Extracellular enzymes are synthesized in inactive forms known as proenzymes.
• Certain enzymes exhibit minor variations in molecular structure yet execute identical functions; they are referred to as isoenzymes or isozymes.
• For instance, lactic dehydrogenase, which catalyzes the conversion of pyruvate to lactate, possesses five more isomeric forms.

Mechanism of action. Fischer (1894) suggested the Lock and Key hypothesis.

Koshland Induced Fit Theory. Lock and Key Theory (Contemplate theory) has been modified and accepted as induced fit theory. This suggests the existence of two groups i.e. buttressing or supporting and catalytic groups on the active site enzyme.

As the substrate gets associated with the buttressing region, the active site changes configurations so that the catalytic group comes to lie opposite to the area where substrate bonds are to be changed.

NEET Biology Nomenclature And Classification Of Enzymes

According to the International Union of Biochemistry (I.U.B—1961) system of classification.

1. Reactions and enzymes catalyzing them are divided into 6 major classes each with 4- 13 subclasses.
2. The enzyme name has two parts—the first name is the substrate. The second ending kinase indicates types of reactions.
3. The enzyme has a systematic Code No. (E.C.). The first digit denotes the class, the second sub-class, the third sub-sub class and the fourth one is for the particular enzyme name.

Thus E.C.2.7.1.1 denotes class two (transferases)-subclass- 7 sub-subclass 1 fan alcohol function as phosphate acceptor). The fourth digit indicates hexokinase.

Enzymes NEET Notes

Major Classes of Enzymes

1. Oxidoreductases. Formerly known as oxidases and dehydrogenase
2. Transferases. Catalyze transfer of one carbon group, aldehyde or ketone, or functional group.
3. Hydrolases. These enzymes cause cleavage of a variety of bonds by the addition of water.
4. Lyases result in the direct removal of groups from the substrate or the break of the bonds without the addition of water.
5. Isomerases. Which catalyze isomeric changes.
6. Ligases or Synthetases. Catalyze linking together of different types of bonds.

NEET Biology Some Terms Regarding Enzymes

Isozymes (Isoenzymes):

Enzymes execute identical duties yet exist in several molecular forms within the same tissue or organ.

For instance, lactate dehydrogenase (LDH) comprises five isoenzymes, while alpha-amylase contains sixteen isoenzymes.

• Denaturation: A process or series of actions that alters the structural configuration of the polypeptide chain of a protein molecule from its original state to a more disordered arrangement. The denatured enzyme exhibits no enzymatic activity.
  Holoenzyme. The enzyme complex is referred to as a holoenzyme.
• Apoenzyme: The protein component of the holoenzyme is thermolabile and colloidal.
• Allosteric locus: A segment of the enzyme where a specific effector or modulator may bind, which can exert either positive or negative effects.
• Allostery (Allosteric inhibition): Modulator-induced alteration of the active site, hence inhibiting substrate binding.

Factors Affecting Enzyme Action

• Effect of enzyme and substrate concentration. Raising the concentration of enzyme increases the rate at which substrate is converted to product, but at high substrate concentration, the enzyme molecules become saturated.
• K1: Disassociation constant of enzyme-inhibitor complex. It applies to competitive inhibitors. Lower K1 is essential for enzyme activity, and higher decreases it.
• Michaelis Constant. (Km) Leonor Michaelis and Mand Menton (1913). It is a constant that indicates the substrate concentration at which the chemical reaction catalyzed by an enzyme attains half of its maximum velocity. The lower the value, the higher the affinity of the enzyme for the substrate.
• Effect of pH. The pH sensitivity of an enzyme depends on how many ionizable R groups are necessary for its activity and its charge. Generally, enzymes function at near-neutral pH.
• Effect of temperature. Temperature above 60°C denatures most proteins or disrupts
  their structure. At low temperatures, enzymatic reactions proceed slowly. The optimum
  temp is 25- 40
• Some blue-green algae live on the surface of glacial ice and have enzymes adapted to temperatures close to freezing point.
• Some bacteria inhabit hot sprigs of the Yellow Stone Park and their enzymes are adapted to function at temperatures 80-85ºC

Classification Of Enzymes NEET Biology

Regulation of Enzyme Action

1. Control at the enzyme level. level DNAl so is termed master feedback.
2. Control at the gene level. molecule inhibition which controls or negatively the feedback synthesis of proteins and therefore enzymes. Proteins are the end products of gene expressions.

NEET Biology Commercially Important Enzymes

1. The biological washing powder enzyme used is Proreases.
2. In brewing, amylases found in germinating barley digest starch in the grain to form malt sugar (maltose).
3. This sugar is fermented by yeast during brewing
4. Amylases used in dishwashing powder remove starch smears from utensils.
5. Rennin plays a role in curdling milk thus helping in cheese making.
6. In leather making, proteases remove hairs from the hide.

Significant Historical Facts of Enzymes

• Krichoffiis (1815): First indicated the occurrence of enzymes in a living system.
• Louis Pasteur (1860): Fermentation of foodstuffs can be brought about by yeast cells.
• Kuhne (1878): First gave the term ‘Enzymes’.
• Buchner (1897): First prepared a pure extract of zymase enzyme from yeast.
• Sumner (1926): Found enzymes to be proteinaceous, crystallized enzyme urease from Jack beans (Canavalia ensifonnis)
• Northelop (1930): Pure crystals of enzyme pepsin and trypsin from gastric and pancreatic juice.
• Monod et al (1965): structure of Allosteric enzymes. These enzymes do not obey Michaelis Menton’s constant i.e. constant.
• Lock and Key hypothesis was given by Emil Fischer (1894) and modified by Koshland (1971) as induced fit theory.
• Arber Nathans and Smith: discovered, the enzyme Restriction Endonuclease.
• Cecil et al (1981) in ribozyme and Altaman et al (1983) for ribonuclease —P found enzyme activity to be present in RNA. (Non-proteinic enzyme) 03 Hansen—Isolated renin Indicate Nobel Laureate.

Classification Of Enzymes NEET Biology

• Enzymes are biological catalysts.
• All enzymes have a specific three-dimensional structure, a part of which is known as an active site.
• An enzyme may have more than one active site.
• Formation of carbonic acid (H2, CO3) from CO, and H,0 in the presence of carbonic anhydrase is 10 million times faster than the non-catalysed reaction.
• Each enzyme can catalyze the change of either a specific substrate or a specific group of a substrate.
• Each enzyme shows its highest activity at a specific pH.
• Cyanide kills an animal by inhibiting cytochrome oxidase, a mitochondrial enzyme essential for cellular
• Respiration. It is an example of non-competitive inhibition of an enzyme.
• The decline in enzyme activity by the allosteric effect of the product is called feedback inhibition Example allosteric inhibition of hexokinase by glucose-6-phosphate.
• Competitive inhibitors are always reversible.
• Non-competitive inhibitors may be reversible or permanent.
  c& Non-reversible inhibitors are always non-competitive.
• According to the Michaelis-Menten equation Km is equal to substrate concentration at which half of maximum velocity is achieved. Michaelis and Menten proposed a
• Hypothesis For Enzyme Action According to the enzyme molecule combines with a substrate complex which further dissociates to form a product and enzyme back
• \(\mathrm{E}+\mathrm{S} \underset{K_2}{\kappa_1} \mathrm{E}-\mathrm{S} \rightarrow{K_3} \mathrm{E}+\mathrm{P} ;\)
• Km (Michaelis-method constant)= \(=\frac{K_3+K_2}{K_1}\)
• They gave the following equation: 
• \(V_o=\frac{V_{\max }(S)}{(S)+K_m}\)
• It is the statement of the quantitative relationship between the initial velocity Vo, the maximum velocity Vmax, and the initial substrate concentrations: all related through Michaelis Menten constant Km
• H- free enzyme
• S = substrate
• HS = enzyme-substrate complex
• I = product
• K1= (he rate constant for ES formation
• K2 = the rate constant for the dissociation of ES into E and S
• K1 is the rate constant for the dissociation of the ES complex into ES and P.

Mechanism Of Enzyme Action NEET Study Material

Quanta to memory

• Kuhne (1878) coined the term enzyme.
• Buchner ( 1897) isolated enzymes for the first time. All components of the cell including the cell wall and cell membrane have enzymes.
• Mitochondria contain a maximum number of enzymes in the cell. (70%)
• The smallest enzyme is peroxidase and the largest is catalase found in peroxisomes.
• Enzyme activity increases from 0°C to optimum temperature and doubles with every 10° rise in temperature. This is called the temperature coefficient (Q10)
• Chemozymes are chemically synthesized enzymes.
• The highest turnover number is of the enzyme carbonic anhydrase. (36 million) with Zn++ as. activator.
• The lowest turnover number is of enzyme lysozymes.
• Mental Activators 
• Na for AT Pase
  Fe „ Catalase, aconitase, cytochrome oxidase
  Zn „ Carbonic anhydrase
  Mg „ Hexokinase
  Mo „ Nitrate reductase
• Enzyme urease isolated from Jack bean Canavalia was crystallized by Sumner in 1926, who proved the protein nature of enzymes.
• Enzymes show 3-D structure.
• Enzymes work in milliseconds and the rate of enzyme of the substrate is as high as 1: 10,00,000.
• Now RNA with catalytic and synthetic functions has been found in a protozoan Tetrahymena thermophila.
• The smaller the Km, the greater the substrate affinity.

Turn over Numbers

• Metal Activators
• Carbonic anhydrase = 3.6 x 106
• Acetyl cholinesestrase = 1.5 x 106
• Urease = 1.0 x l06
• Amylase = 10 x 10s
• Lactic acid dehydrogenase = 6.0 x 104
• Chymotrypsin = 6.0 x 103
• Lysozyme = 3.0x 101

Enzymes Identified with Hereditary Disease

Multiple Choice Questions on Enzymes – NEET Biology

Question 1. As the temperature changes from 30 to 45’c the rate of enzyme activity will:

1. Decrease
2. First decrease and then increase
3. First increase and then decrease
4. Increase.

Answer: 3. First increase and then decrease

Question 2. Which one inactivates an enzyme by changing the enzyme’s shape?

1. Non-competitive inhibitor
2. Competitive inhibitor.
3. Coenzyme
4. All the above.

Answer: 1. Non-competitive inhibitor

Question 3. A non-proteinic enzyme is :

1. Lysozyme
2. Zymase
3. Papain
4. Rna ase-p.

Answer: 4. Rna ase-p.

Question 4. Which of the following belongs to class 5 of the cubic system of classification of enzymes?

1. Isomerase
2. Ligases
3. Transferase
4. Lyases.

Answer: 1. Isomerase

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General mechanism of Enzymes NEET MCQs Question 5. Which does inactivate by denaturation in it?

1. Allosteric inhibitor
2. Competitive inhibitor
3. Irreversible inhibitor
4. None of the above.

Answer: 1. Allosteric inhibitor

Question 6. Most of the enzymes are secreted in an inactive form, otherwise, they will be destroyed.

1. Cell proteins
2. Cell dna
3. Cell mitochondria
4. Cell wall and membrane.

Answer: 1. Cell proteins

Question 7. The fastest enzyme is :

1. Pepsin
2. Trypsin
3. Catalase
4. Carbonic anhydrase.

Answer: 4. Carbonic anhydrase.

Question 8. Buchner isolated

1. Siamese
2. Zymase
3. Zeatinase
4. Ferment.

Answer: 2. Zymase

Question 9. The best example of extracellular enzymes (exoenzymes) is:

1. Nucleases
2. Digestive enzymes
3. Succinic dehydrogenase
4. None of the above.

Answer: 2. Digestive enzymes

Question 10. Enzymes bring about hydrolysis of esters and peptides are :

1. Transferases
2. Lyases
3. Hydrolases
4. Ligase.

Answer: 3. Hydrolases

General mechanism of Enzymes NEET MCQs Question 11. Examples of amine online are:

1. Arginase
2. Lactase
3. Zymase
4. Lipase.

Answer: 1. Arginase

Question 12. Energy must be added to a chemical reaction to start. This energy is known as the energy of :

1. Entropy
2. Activation
3. Enthalpy
4. Oxidation.

Answer: 2. Activation

Question 13. Which level of ‘x’ represents the usable energy yield?

1. 1
2. 2
3. 3
4. 4.

Answer: 2. 2

Question 14. Which segment of ‘x’ represents the energy of activation?

1. 1
2. 2
3. 4
4. 4

Answer: 1. 1

Question 15. The chemical reaction shown in the world be accelerated by all of the following processes:

1. Heating A and b together
2. Applying pressure to a and b
3. Adding an appropriate catalyst
4. Increase the conc. Of c.

Answer: 4. Increase the conc. Of c.

Enzymes Recommended MCQs NEET Questions Question 16. In most of the metabolic pathways, all needed enzymes are arranged together, in a multienzyme complex within:

1. Solution of atp
2. Membrane
3. Quarternary protein
4. Coenzyme.

Answer: 2. Membrane

Question 17. A non-protein organic part attached firmly to an apoenzyme is called :

1. Cofactor
2. Activator
3. Metallic group
4. Coenzyme.

Answer: 1. Cofactor

Question 18. Which is an enzyme that joins two segments of replicated dna?

1. Ligase
2. Lyase
3. Endonuclease
4. None of the above.

Answer: 1. Ligase

Question 19. Apoenzyrne and coenzyme collective produce :

1. Holoenzyme
2. Enzyrne-product complex
3. Cofactor
4. Prosthetic group.

Answer: 1. Holoenzyme

Question 20. Minimum number of amino acids to make an enzyme is:

1. 50
2. 150
3. 500
4. 5000.

Answer: 1. 50

Question 21. Fmn and fad are coenzymes derived from :

1. Ascorbic acid
2. Riboflavin
3. Thiamine
4. Pyridoxine.

Answer: 1. Ascorbic acid

Enzymes Recommended MCQs NEET Questions Question 22. Enzymes differ from inorganic catalysts in having:

1. High diffusion rate
2. High-temperature requirement
3. Proteinaceous structure
4. Tendency to become inactivated.

Answer: 3. Proteinaceous structure

Question 23. Active sites of enzymes are composed of :

1. Sugm molecule
2. Metallic ions
3. Organic co-factors
4. Amino acids.

Answer: 4. Amino acids.

Enzyme MCQ for NEET Question 24. Pepsin best works at :

1. Ph 7.00
2. Ph 8.5
3. Ph.00
4. Ph 8.00.

Answer: 3. Ph.00

Question 25. Of the following chemicals, the one that is classified as an enzyme is :

1. Galactose
2. Lipids
3. Manganese dioxide
4. Protease.

Answer: 4. Protease.

Question 26. Ribozyme is :

1. Rna without sugar
2. Rna with extra phosphate
3. Rna having enzymatic activity
4. All of the above.

Answer: 3. Rna having enzymatic activity

Enzymes Recommended MCQs NEET Questions Question 27. Allenzymes:

1. Are amino acids
2. Act best at 60ºc
3. Act best at 7 ph
4. Are proteins.

Answer: 4. Are proteins.

Question 28. At high temperatures, the enzyme is :

1. Denaturated
2. Killed
3. Slightly activated
4. Inactivated.

Answer: 1. Denaturated

Question 29. Inorganic catalyst attached to an enzyme is :

1. Apoenzyme
2. Coenzyme
3. Inhibitor
4. Activator.

Answer: 4. Activator.

Question 30. Enzymes are polymers of :

1. Fatty acids
2. Amino acids
3. Hexose sugar
4. Inorganic phosphate.

Answer: 2. Amino acids

MCQs on Enzymes Question 31. One is not correct :

1. All enzymes are thermolabile
2. All enzymes are biocatalysts
3. All enzymes are proteins
4. All proteins are enzymes.

Answer: 4. All proteins are enzymes.

Question 32. Match the tennis in column 1 with suitable terms in column 2

Which of the following is correct?

1. 1-G, 2-E, 3-A, 4-B, 5-F,6-C
2. 1-G, 2-E, 3-B, 4-C, 5-D, 6-F
3. 1-G, 2-A, 3-D, 4-F, 5-B, 6-A
4. 1-G, 2-E, 3-D, 4-B, 5-4 5-F.

Answer: 3. 1-G, 2-A, 3-D, 4-F, 5-B, 6-A

Question 33. Modulation:

1. Inhibit enzyme activity
2. Stimulate enzyme activity
3. Function as coenzymes
4. Both 1 and 2.

Answer: 4. Both a and b

MCQs on Enzymes Question 34. K. Indicates :

1. Competitive inhibition
2. Denaturation of enzymes
3. Reaction velocity
4. All of these.

Answer: 3. Reaction velocity

Question 35. Which is susceptible to feedback inhibition?

1. Zymogen
2. Zymase
3. Glucokinase
4. Hexokinase.

Answer: 4. Hexokinase.

Question 36. Ribozyme was discovered by :

1. Kuhne
2. Because
3. Cech at all
4. Altman at all

Answer: 3. Cech at all.

Question 37. An enzyme that brings about a change in side group without altered composition:

1. Isomerase
2. Epimease
3. Mutase
4. Esterase.

Answer: 3. Mutase

Question 38. Enzymes functional in cells are:

1. Inducible, constitutive, and repressible
2. Inducible and repressible
3. Inducible only
4. Repressible on1y.

Answer: 1. Inducible, constitutive, and repressible

Question 39. Flavoproteins in cellular oxidation are called:

1. Splitting enzyme
2. Redox enzyme
3. Uricolytic enzyme
4. Yellow enzyme.

Answer: 4. Yellow enzyme.

Enzymes MCQ Objective Questions  Question 40. The presence of enzymes in the urine is called :

1. Enzymuria
2. Enzymopenia
3. Enzymopathy
4. None of the above.

Answer: 1. Enzymuria

Question 41. Elisa test used in detecting:

1. Antigen
2. Antibody
3. Hormone
4. All of the above.

Answer: 4. All of the above.

Question 42. A person suffering from a.tr.d.s is a resident of an area that is exposed to radio waves which test is preferred to detect h.i.v. Infection.

1. R.i.a (radio immune assay)
2. H.i.v. Test.
3. E.l.i.s.a. Test
4. All of the above.

Answer: 3. E.l.i.s.a. Test

Question 43. Which of the following curve profiles show changes in the velocity (v) of an enzyme-catalyzed reactions at different pH values :

Answer: 1. 

Question 44. According to Koshland:

1. The enzyme is never destroyed
2. The enzyme is a rigid molecule
3. The catalytic site of the enzyme is rigid
4. Catalytic sites can be influenced by the presence of substrate.

Answer: 4. Catalytic sites can be influenced by the presence of substrate.

Enzymes MCQ Objective Questions  Question 45. According to Michaelis constant, the value of v is expressed as

1. [Latex]v=\frac{v_{\max } \times(s)}{k_m+(s)}[/latex]
2. [Latex]v=\frac{k_m+(s)}{v_{\max } \times(s)}[/latex]
3. [Latex]\mathrm{v}=\frac{\mathrm{v}_{\max } \times \mathrm{k}_{\mathrm{m}}}{[\mathrm{s}]}[/latex]
4. [Latex]\mathrm{v}=\frac{\mathrm{k}_{\mathrm{m}} \times(\mathrm{s})}{\mathrm{v}_{\max }} .[/Latex]

Answer: 2. [Latex]v=\frac{k_m+(s)}{v_{\max } \times(s)}[/latex]

Question 46. Enzymes catalyzing the hydrolysis of ester and peptide by the addition of water are known as:

1. Transferases
2. Hydrolases
3. Isomerases
4. Oxidation-reduction enzymes.

Answer: 2. Hydrolases

Question 47. Model of fisher implies that;

1. The active site is flexible and adjusts to the substrate
2. The active site requires the removal of PO, group
3. The active site is complementary in shape to that of the substrate
4. None of the above.

Answer: 3. The active site is complementary in shape to that of the substrate.

Question 48. C-amp mediated “cascade model” of enzyme regulation was proposed by :

1. Fisher
2. Sutherland
3. Sumner
4. Koshalnd.

Answer: 2. Sutherland

Question 49. The substrate combines more rapidly with the enzyme when:

1. Km is high
2. Km is low
3. Ki is high
4. Ki is low.

Answer: 2. Km is low