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Genetic drift is a change in gene frequency within a population due to chance instead of natural selection. If the population is small, then there can be considerable genetic drift, which can change the gene frequency quite drastically. Think of the genetic variation of a population as a bowl of jelly beans with all sorts of colors, representing healthy genetic variation.
Genetic Drift Defined. Populations of organisms are constantly changing and adapting to their environment. Drastic changes in environmental conditions can sometimes cause drastic changes to the gene pool of the population. Genetic drift is when chance events cause changes in frequencies of alleles in a population. Alleles are the genetic variations in a population, and they are the driving force behind the evolution of that population. The smaller the population, the greater the impact genetic drift will have.