Q.Briefly describe Sewal-Wright effect.

The Sewall Wright effect = genetic drift: random changes in allele frequency, significant in small populations, that alter the gene pool by chance rather than by selection.

Genetic drift is one of the forces that can change the allele frequencies of a population and so bring about evolution. It was studied in detail by the geneticist Sewall Wright, and hence random genetic drift is also called the Sewall Wright effect.

Explanation:

• In any population, the passing of alleles from one generation to the next involves an element of chance (which gametes happen to unite, which individuals happen to survive and reproduce).
• In a large population these chance fluctuations average out and allele frequencies stay fairly stable (as the Hardy–Weinberg law describes).
• But in a small population, chance events have a big effect: by accident some alleles may fail to be passed on, or a few individuals may contribute disproportionately, so certain alleles become more common and others may be lost entirely — with no reference to whether they are useful. This random change in allele frequency is genetic drift / the Sewall Wright effect.

Consequences:

• It can reduce genetic variation in the population.
• It can fix or eliminate alleles by chance, and so change the genetic character of the population over generations. …