Question

Differentiate natural selection from genetic drift in terms of: a) the effect of population size b) neutrality c) fitness of traits d) adaptations

Answer 1

Answer-

Genetic drifftis defined as " the nondirectional, random fluctuations in the allele frequencies in the gene pool of small populations, occurring by chance and not in adaptive direction." Whereas, Natural selection is the force which ensures differential contribution of alleles of a gene to the gene pool of a population in the next generation and maintains polymorphism in the genotypes of individuals generation after generation. As an example, when allele A makes an organism more efficient in reproduction than its allele a, the frequency of allele A gradually increases in the gene pool generation after generation and the frequency of allele a gradually decreases. Thus, Natural selection is a creative force and is achieved either by increased rate of reproduction or by the decreased vulnerability to environmental agents responsible for mortality.

Difference between Genetic drifft and natural selection-

A) Genetic drift operates in small populations, whereas natural selection operates in large populations.

B) Most mutation or genetic variation at molecular level are of neutral or nearly neutral value. They lack adaptive signifficance and are ffixed in the population or are eliminated by genetic drift. It means, it is only chance or random drift which delineates a novel collection of mutants into a group, divergent from the parental population. It also acknowledges that many mutations are deleterious and are eliminated by natural selection.

C) Genetic drift leads to loss of genetic variation and favours Homozygosity by fixing or eliminating the other alleles. Natural selection, on the other hand supports heterozygosity in the population because of heterozygous superiority. According to natural selection, only those individuals could survive which can adapt better to the changing environment.

D) Genetic drift does not support adaptive changes in the frequency of alleles. Natural selection favours in the frequency of those alleles that provide reproductive advantage and leads to adaptive evolution.