Genetic drift

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Adaptation
Genetic drift
Gene flow
Mutation
Natural selection
Speciation

Introduction
Evidence
Evolutionary history of life
History
Level of support
Modern synthesis
Objections / Controversy
Social effect
Theory and fact

Cladistics
Ecological genetics
Evolutionary anthropology
Evolutionary development
Evolutionary psychology
Molecular evolution
Phylogenetics
Population genetics
Systematics

Genetic drift or allelic drift is the change in the frequency of a gene variant (allele) in a population due to random sampling. The alleles in the offspring are a sample of those in the parents, and chance has a role in determining whether a given individual survives and reproduces. A population's allele frequency is the fraction of the copies of one gene that share a particular form.[1]

Genetic drift is an important evolutionary process, which leads to changes in allele frequencies over time. It may cause gene variants to disappear completely, and thereby reduce genetic variation. In contrast to natural selection, which makes gene variants more common or less common depending on their reproductive success,[2] the changes due to genetic drift are not driven by environmental or adaptive pressures, and may be beneficial, neutral, or detrimental to reproductive success.

The effect of genetic drift is larger in small populations, and smaller in large populations. Vigorous debates wage among scientists over the relative importance of genetic drift compared with natural selection. Ronald Fisher held the view that genetic drift plays at the most a minor role in evolution, and this remained the dominant view for several decades. In 1968 Motoo Kimura rekindled the debate with his neutral theory of molecular evolution, which claims that most changes in genetic material (although not necessarily changes in phenotypes) are caused by genetic drift.[3]

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