Random Genetic Drift: A Non-directional Force of Evolution

Abstract

Evolution is a corner stone of biology. In terms of genetics, it is defined as a change in genetic composition of populations. A population has two attributes: Gene frequency proportion of different alleles of a gene in a population; Gene pool- sum total of genes in the reproductive gametes of a population (considered as gametic pool). When the population is evolving and under-going microevolutionary changes, different elemental forces operate to bring about these changes: mutation, natural selection, migration and random genetic drift. The first three forces have one quality in common, they usually operate in directional fashion to change allele frequencies progressively from one value to the other. When other factors are not opposing, these factors can lead to fixation of one allele and elimination of others. In case polymorphism is balanced, they can lead to equilibrium between two or more alleles. On the other hand, there is another factor that brings about the changes in allele frequency in nondirectional manner and has no predictive constancy from generation to generation. It is known as random genetic drift which arises from variable sampling of gene pool in each generation. It operates in small populations and causes allele frequency changes due to chance events causing random fluctuation in allele frequency occurring because of sampling errors. It may lead to fixation or elimination of a particular allele which causes increase in homozygosity. Sewall Wright discussed the role of genetic drift in small populations with particular