Question

Genetic drift operates in [NEET 2016, Phase II]

(a) small isolated population

(b) large isolated population

(c) non-reproductive population

(d) slow reproductive population

Answer/Explanation

Ans. (a)
The genetic drift is a drastic change in allele frequency when population size is very small. Its effects are more marked in a small isolated population.

Question

Industrial melanism is an example of [CBSE AIPMT 2015]

(a) Neo Darwinism

(b) Natural selection

(c) Mutation

(d) Neo Lamarckism

Answer/Explanation

Ans. (b)
Within a periad of years in industrial or polluted areas, the dark species has almost replaced the light species. This is called industrial melanism beceuse of its association with the sooty atmosphere of industry. It is an example of natural selection.

Question

 Variation in gene frequencies within populations can occur by chance rather than by natural selection. This is referred to as [NEET 2013]

(a) genetic flow

(b) genetic drift

(c) random mating

(d) genetic load

Answer/Explanation

Ans. (b)
Genetic drift is a random change in allele frequencies over the generations. It is brought by chance alone. Gene flow or gene migration is the physical movement of alleles into and out of a population.

Question

 In the case of peppered moth (Biston betularia), the black-coloured form became dominant over the light-coloured form in England during industrial revolution. This is an example of [CBSE AIPMT 2009]

(a) natural selection whereby the darker forms were selected

(b) appearance of the darker coloured individuals due to very poor sunlight.

(c) protective mimicry

(d) inheritance of darker colour character acquired due to the darker environment.

Answer/Explanation

Ans. (a)

The given case is an example of natural selection. As a result of struggle for existence only those organisms could survive, which have favourable variations to adapt to the environmental conditions. With so many variations in population of species the struggle for existence results in survival of the fittest.
The survival of the fittest is the result of selection and proliferation of only those organisms, which were most suitably adapted to the environment and most successful in mating, i.e. natural selection.

Question

 Which one following scientists name is correctly matched with the theory put forth by him? [CBSE AIPMT 2008]

(a) Weismann-Theory of continuity of germplasm

(b) Pasteur-Inheritance of acquired characters

(c) De vries-Natural selection

(d) Mendei-Theory of pangenesis

Answer/Explanation

Ans. (a)

The correct theory is the Weismam Theory of continuity of germplasm. Rest of the theories were proposed by Scientist Theory Pasteur-Germ theory of diseaseCharles Darwin-Theory of natural selection Lamarck-Inheritance of accquired characters Hugo de Vries-Mutation theory Mendel-Laws of inheritance Darwin-Theory of pangenesis

Question

 Select the correct statement from the following given options. [CBSE AIPMT 2007]

(a) Darwinian variations are small and directionless

(b) Fitness is the end result of the ability to adlapt and gets selected by nature

(c)All mammals except whales and camels have seven cervical vertebrae

(d) Mutations are random and directional

Answer/Explanation

Ans. (b)
Fitness (survival of the fittest) is a result of selection and proliferation af only those organisms which were most suitably adapted to the environment and get selected by nature.

Question

 De Vries gave his mutation theory on organic evolution while working on [CBSE AIPMT 2005]

(a) Pisum sativum

(b) Drosophila melanogaster

(c) Oenothera lamarckiana

(d) Althea rosea

Answer/Explanation

Ans. (c)

Hugo de Vries [1848-1935] proposed mutation theory for the formation of new species. He came to conclude this theory while working on Denathera lamarchiana evening primrose.
According to him, new species are not formed by continuous variations but by sudden appearance of variations which he assigned as mutations. He stated that these mutations are heritable and persist in successlve generations.

Question

 Which one of the following phenomena supports Darwin’s concept of natural selection in organic evolution? [CBSE AIPMT 2005]

(a) Development of transgenic animals

(b) Production of ‘Dolly’, the sheep by cloning

(c) Prevalence of pesticide resistant insects

(d) Development of organs from ‘stem cells’ for organ transplantation

Answer/Explanation

Ans. (c)
According to Darwin’s concept of natural selection the arganisms which are provided with favourable variations would survive because, they are the fittest to face their surrounding, while the organisms which are unfit for surrounding variations are destroyed. Prevalence of pesticide resistant insects is due to the adaptability of these insects for the changes in environment. (due to use of pesticides).

Question

 Darwin in his ‘Natural Selection Theory’ did not believe in any role of which one of the following in organic evolution? [CBSE AIPMT 2003]

(a) Discontinuous variations

(b) Parasites and predators as natural enemies

(c) Survival of the fittest

(d) Struggle for existence

Answer/Explanation

Ans. (a)

Natural theory of Darwin did not believe in any role of discontinuous variations. Darwin called the variations as ‘sports’. While, Hugo de Vries used the term mutation to these variations. These variations are sudden heritable changes which can occur in any stage of development.

Question

In a random mating population in equilibrium, which of the following brings about a change in gene frequency in a non-directional manner? [CBSE AIPMT 2003]

(a) Migration

(b) Mutation

(c) Random drift

(d) Selection

Answer/Explanation

Ans. (b)

Given certain conditions, the allele frequencies remain constant from generation to generation. Under these conditions, a population would be in equilibrium and there will be no evolutionary change. However, many evolutionary changes usually occur following the appearance of new alleles and source of this is mutation.

Question

 Random genetic drift in a population probably results from [CBSE AIPMT 2003]

(a) large population size

(b) highly genetically variable individuals

(c) interbreeding within this population

(d) constant low mutation rate

Answer/Explanation

Ans. (b)
Genetic drift or Sewall Wright effect is statically significant change in population gene frequencies resulting by chance and not from natural selection, emigration or immigration. In simple words, random loss of alleles is known as genetic drift.

Question

 Which one of the following sequences was proposed by Darwin and Wallace for organic evolution? [CBSE AIPMT 2003]

(a) Variations, natural selection, overproduction, constancy of population size

(b) Overproduction, variations, constancy of population size, natural selection

(c) Variations, constancy of population size, overproduction, natural selection

(d) Overproduction, constancy of population size, variations, natural selection

Answer/Explanation

Ans. (b)

Though living organisms tend to multiply geometrically, the number of individuals of a species tend to remain constant over a long period of time. Out of heterogenous population (due to the variation) best adapted individuals are selected by nature.

Question

 Genetic drift operates in [CBSE AIPMT 2002]

(a) small isolated population

(b) large isolated population

(c) fast reproductive population

(d) slow reproductive population

Answer/Explanation

Ans. (a)

Genetic drift refers to changes in allele frequencies of a gene pool due to chance. Though it operates both in large and small populations, it is expected to be significant only in small populations, where alleles may become extinct or get fixed by chance alone.

Question

 Reason of diversity in living being is [CBSE AIPMT 2001]

(a) mutation

(b) gradual change

(c)long term evolutionary change

(d) short term evolutionary change

Answer/Explanation

Ans. (c)

Though mutation provides the source of variation, the diversity in living beings is due to the natural selection of variations and consequent evolutionary change over a long periods of time.

Question

 Darwin’s theory of pangenesis shows similarity with theory of inheritance of acquired characters then what will be correct according to it? [CBSE AIPMT 2001]

(a) Useful organs become strong and developed while useless organs become extinct. These organs help in struggle for survival

(b) Size of organs increase with ageing

(c) Development of organs is due to will power

(d) There should be some physical basis of inheritance

Answer/Explanation

Ans. (d)

According to both the views, something is passed from parent to offspring which causes development of specific characters, i.e. all that has been acquired by the organism during its life time is preserved by generation and transmitted to offsprings in form of pangenes is or gemmules.

Question

 The presence of gill slits, in the embryos of all vertebrates, supports the theory of [CBSE AIPMT 1995]

(a)biogenesis

(b) recapitulation

(c) metamorphosis

(d) organic evolution

Answer/Explanation

Ans. (a)
The theory of recapitulation’ or ‘Biogenetic law’, propounded by Haeckel states that an individual organism in its development (ontogeny) tends to repeat the stages passed through by its ancestors(phylogenyl. During the life history of frog, tadpole larva resembles fishes, the ancestors of Amphibia. The presence of gill clefts in vertebrate embryo provides a strong evidence in support of organic evolution.

Question

 Which one does not favour Lamarckian concept of inheritance of acquired characters? [CBSE AIPMT 1994]

(a) Lack of pigment in cave dwellers

(b) Absence of limbs in snakes

(c) Presence of webbed toes in aquatic birds

(d) Melanization of peppered moth in industrial areas

Answer/Explanation

Ans. (d)

Lamarck believed in direct influence of environment on the individual. Lamarckian postulate of use and disuse of organs is supported by rudimentary eyes of cave dwellers, webbed feet of swimming bird, elongated limbless body of snake, vestigial organs of living animals, etc. Biston betularia(peppered moth) shows industrial melanism and demonstrates natural selection.

Question

 Frequency of a character increases when it is [CBSE AIPMT 1994]

(a) recessive

(b) dominant

(c) inheritable

(d) adaptable

Answer/Explanation

Ans. (d)
According to Darwin, the variations are continuous and those which are helpful in the adaptations of an organism towards its surrounding would be passed on to the next generation. In the offsprings, these modifications become more pronounced if they are exposed to similar stress of the environment as faced by their parents.

Question

 Theory of natural selection dwells on [CBSE AIPMT 1993]

(a) role of environment in evolution

(b) natural selection acting on favourable variations

(c)changes in gene complex resulting in heritable variations

(d) None of the above

Answer/Explanation

Ans. (b)
According to Darwin’s theory of natural selection, in the struggle for existence, only those individuals survive which possess the most useful variations. Useful variations present in the surviving individuals are passed on to the next. generation. Next generation repeats the process of development of variations and natural selection.

Question

Weismann cut off tails of mice generation after generation but tails neither disappeared nor shortened showing that [CBSE AIPMT 1993]

(a) Darwin was correct

(b) tail is an essential organ

(c) mutation theory is wrong

(d) Lamarckism was wrong in inheritance of acquired characters

Answer/Explanation

Ans. (d)
Lamarckian theory of inheritance of acquired characters was discarded by Weismann, while experimenting on mice. He cut the tails of mice for 80 generations but no single mouse was born without tail. Weismann formulated his famous ‘Theory of continuity of germplasm’, according to which only those characters, whatever be their origin and nature, that could affect germplasm are heritable and others are not.

Question

 Basic principles of embryonic development were pronounced by[CBSE AIPMT 1990]

(a) Von Baer

(b) Weismann

(c) Haeckel

(d) Morgan

Answer/Explanation

Ans. (a)

The basic laws or principles of embryonic development were given by von Bleer in 1828. According to his theory during embryonic development generalised features brain, spinal cord etc. appeared earlier than special features like hair. Haeckel (1B66) propounded The theory of recapitulation or Biogenetic law.

Question

‘ Continuity of germplasm’ theory was given by [CBSE AIPMT 1989]

(a) De Vries

(b) Weismann

(c) Darwin

(d) Lamarck

Answer/Explanation

Ans. (b)

August Weismann, a German scientist formulated his famous ‘Theory of continuity of germplasm in 1886, on experimenting with mice. His theory states that inheritance in multicellular organisms takes place by means of germ cells i.e. egg and sperm cells only.

Question

 Theory of inheritance of acquired characters was given by [CBSE AIPMT 1989]

(a) Wallace

(b) Lamarck

(c) Darwin

(d) De Vries

Answer/Explanation

Ans. (b)

Jean Baptiste de Lamarck (1744-1829) was the greatest of French naturalists, who for the first time suggested a complete theory of evolution. Lamarckian theory is also known as Theory of inheritance of acquired characters’ or ‘Theory of use and disuse of organs’.

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