Genetic Drift & Gene Flow

Genetic drift and gene flow are two mechanisms involved in evolutionary processes.

Genetic Drift

Genetic drift is a change in the allelic frequency within a population due to random chance. It is especially apparent within small breeding populations.

Genetic drift occurs when random chance results in certain alleles being passed on to future generations, while others are passed on at a lower rate, or even lost from the population.

For example, consider a population that has individuals with either brown or blue eyes. Suppose that eye color has no impact on reproductive success. If a random event, such as a natural disaster, resulted in the death of all blue-eyed individuals, then this allele would no longer be present in the population. This is an example of genetic drift because there was no selection involved in the loss of the allele from the population.