In population genetics, what is genetic drift and when is it most impactful?

• A. Natural selection acting on traits
• B. Random changes in allele frequencies, especially in small populations
• C. Gene flow moving alleles between populations
• D. Mutation introducing new alleles

Answer: (B)

Genetic drift is the random fluctuation of allele frequencies from one generation to the next due to chance events rather than natural selection. Because these changes are random, they can move alleles toward fixation or loss independently of whether those alleles confer any advantage. This effect is strongest in small populations, where each individual represents a larger fraction of the gene pool. A few random births, deaths, or sampling differences can dramatically shift which alleles are common or rare, and over time drift can reduce genetic variation within the population and increase divergence between populations.

This differs from natural selection, which changes allele frequencies because certain traits influence survival and reproduction; it differs from gene flow, which involves the movement of alleles between populations and tends to homogenize populations; and it differs from mutation, which introduces new alleles rather than randomly altering existing frequencies.