Definition of Genetic Drift
Genetic drift is a phenomenon in which there is a variation in the frequency of an allele in a population. This change occurs as certain genes get randomly selected. Sometimes, it happens that there is a small change in DNA (mutation). But this mutation has generally no effect on the fitness of an organism. Genetic drift is most common in those populations which have less number of individuals but it can occur in larger populations too.
Example of Genetic Drift:
Take an example of 100 rabbits which are existing in a population in red, brown, tan, black, white, and grey. The disease comes and 98 rabbits succumb to it. Only two are left in red and grey color. The gene resultantly has drifted from 6 alleles to only 2 alleles.