Question

What is genetic drift ? Give its significance in evolution.

Answer 1

Hint: The process of changing frequencies of genes from one generation to another is known as genetic drift. This happens due to the number of individuals in any population is finite, and thus the frequency that the gene may change in the following generation by accidents of sampling, just as it is possible to get more or fewer than 50 “ heads” in a 100 throws of coin simply by chance.

Complete answer:
Genetic drift : Genetic drift is a mechanism of evolution in which change occurs due to “sampling error “ in selecting the alleles for the next generation from the gene pool of the current generation. Although genetic drift happens in populations of all sizes, its effect tends to be stronger in small populations.
Significance of Genetic drift in Evolution :
Natural selection is an important mechanism of evolution. But this is not the only mechanism, sometimes evolution just happens by chance.
In population, evolution is defined as a change in the frequency of alleles ( versions of a gene ) in a population over time. So, evolution is any shift in allele frequencies in a population over generations, whether that shift is due to natural or some other evolutionary mechanism, and whether that shift makes the population better-suited for its environment or not.
Genetic drift can have major effects when a population is sharply reduced in size by natural disaster (bottleneck effect) or when a small group splits off from the main population to found a colony.
> Founder effect : The founder effect is an extreme example of drift, one that occurs when a small group of individuals breaks off from a larger population to establish a colony. The new colony is isolated from the original population, and the founding individuals may not represent the full genetic diversity of the original population. That is, alleles in the founding population may be present at different frequencies than in the original population, and some alleles may be missing altogether.

> Representation of founder effect : The coloured balls represent two alleles for a specific locus which are present in hypothetical population, once a random subgroup of a population become separated from its ancestral population, the allele frequencies in the two groups, subsequent generations can diverge widely within a relatively short period of time as a consequence of a purely random selection of alleles for reproduction.

Note: Unlike natural selection, genetic drift does not depend on an allele’s beneficial or harmful effects. Instead, drift changes allele frequencies purely by chance, as random subsets of individuals ( gametes of those individuals) are sampled to produce the next generation.
The founder effect and the bottleneck effect are cases in which a small population is formed from a larger population.