Drift: Introduction

Abstract

Abstract Genetic drift is the random change in allele frequencies by the chance success of some alleles relative to others. Genetic drift is more important in small populations, where chance plays stronger role. If the population size is small enough relative to the strength of selection, genetic drift can sometimes cause slightly deleterious alleles to rise in frequency or beneficial alleles to be lost from a population. Drift can lead to the fixation or loss of alleles, and therefore drift can contribute to the loss of genetic variation. As a consequence, genetic drift in small populations is a source of concern for the future evolutionary potential for some endangered species. Key Concepts: Alleles may increase or decrease in frequency by chance. The effects of chance on allele frequency change are most pronounced in small populations. Genetic drift tends to lead to fixation or loss of alleles over time, and therefore contributes to the loss of genetic variation. If the population size is small enough relative to the strength of selection, genetic drift can cause the fixation of deleterious alleles or loss of beneficial alleles. Genetic drift can cause genetic divergence between species or populations. Most genetic differences between species are probably due to genetic drift. Genetic drift is nonadaptive and nondirectional.