Biology: genetic drift

Tutoring biology, mechanisms of evolution arise. The tutor mentions genetic drift.

Genetic drift is a change of genetic ratios in a population – for example, the percent of individuals who have brown eyes vs blue. Importantly, genetic drift occurs by chance, not based on fitness for survival.

The process of genetic drift could be modeled by the following situation: let’s imagine two clans, Clan1 and Clan2, are planning to migrate from Mountain A to Mountain B by crossing a bridge. They decide that Clan1 will cross first, then Clan2. Just after Clan1 crosses, a mild earthquake collapses the bridge; therefore, Clan1 is now on Mountain B, while Clan2 remains on Mountain A. With the bridge gone, the two clans can no longer mingle, so become separate populations.

From now on, the population on Mountain A will abundantly display Clan2’s genes, but not Clan1’s. The opposite will be true on Mountain B: Clan1’s genes will be the only ones expressed from now on. Yet, before Clan1 crossed the bridge, both Clan1 and Clan2 lived on Mountain A, so Mountain A harboured both genetic profiles.

Genetic drift tends to decrease genetic variation in a given population, and can lead to dramatic differences in genetic profiles between isolated populations. By itself it doesn’t cause evolution, but can lead to separate populations taking different evolutionary directions given their specific characteristics.

Source:

genome.gov

sciencedirect.com