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Evolutionary Theory

Author(s): Tadzia GrandPré, PhD, Nancy Moreno, PhD, and Lisa Marie Meffert, PhD

Genetic Drift

Most populations are limited in size, and many can be very small. In small populations, dramatic changes in allele frequency can occur simply by chance. This is an evolutionary mechanism called genetic drift. The smaller the population, the greater the effect of genetic drift on the population's gene pool. When only a random subset of individuals contribute to the next generation, the statistical properties of sampling cause random deviations in allele frequency and consequent genotypic frequency.