Which evolutionary mechanism changes allele frequencies by chance, especially in small populations?

Fact

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Genetic drift is the random change in allele frequencies from one generation to the next. It arises partly from chance in reproduction: not every individual passes on genetic variants in equal proportions, even when those variants provide no particular advantage. Its effects are strongest in small populations, where an allele can quickly disappear or become the only version present. Founder events and population bottlenecks are important examples of this process. Unlike natural selection, genetic drift does not direct change according to whether a trait improves survival or reproductive success.