Class 10 Science Biology Heredity and Evolution



Which of the following statements is not true with respect to variation?
(a)
All variations in a species have equal chance of survival.
(b)
Change in genetic composition results in variation.
(c)
Selection of variants by environmental factors forms the basis of evolutionary processes.
(d)
Variation is minimum in a sexual reproduction.
(e)
Both A and D
Correct answer: (e) 
Solution: Variations refer to divergence among individuals of a group or divergence of the individual from other individuals of the same species which do not result from sex, age or nutritional status. Mutations, random inheritable changes in structure and number of DNA molecules in reproductive cells of organisms, generate the genetic variations among individuals of a population. This makes statement B correct. These random variations are acted upon by natural selection that favors only those which confer survival and/or reproductive advantage to the individuals over others. Accumulation of these adaptive variations in lineages over generation makes them better adapted to existing environmental conditions. Accumulation of adaptive changes in population’s genetic makeup through successive generations leads to evolution which makes statement C correct. This makes statement A incorrect as irrespective of random nature of mutations, natural selection favors only adaptive variations i.e. the nonadaptive/ negative variations are not favoured. Statement D is incorrect as crossing over during gametogenesis and random fusions of gametes during syngamy produce maximum variations by sexual reproduction. Both options A and D are incorrect. 

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