Genetic drift is a mechanism of evolution in which allele frequencies of a population change over generations due to chance (sampling error).
Genetic drift occurs in all populations of non-infinite size, but its effects are strongest in small populations.
Genetic drift may result in the loss of some alleles (including beneficial ones) and the fixation, or rise to frequency, of other alleles.
Genetic drift can have major effects when a population is sharply reduced in size by a natural disaster (bottleneck effect) or when a small group splits off from the main population to found a colony (founder effect).
