Genetic Drift

Genetic drift is random changes in allele frequencies in a population over time. The effect of genetic drift on evolutionary change is strongest in small populations due to the increased chance of the fixation or disappearance of alleles. Genetic drift is always happening, but scientists often talk about two specific scenarios involving genetic drift: 

• Founder Effect occurs when new populations become isolated from a parent population. This isolated population (‘founders’) carries only a subset of genetic variation of the original population. 

• A Bottleneck is when there is a dramatic reduction in the size of a population (e.g. due to chance environmental changes), which results in reduced genetic variation in the population.