What is genetic drift?

• A. Random changes in allele frequencies in a population due to selection
• B. Nonrandom mating
• C. Random changes in allele frequencies in a population, especially in small populations.
• D. Migration of individuals between populations

Answer: (C)

Random fluctuations in allele frequencies from one generation to the next, not caused by differences in fitness. In small populations, these random sampling effects are amplified, so alleles can become more common or disappear purely by chance. This is why genetic drift can quickly alter the genetic makeup and even fix or lose alleles over time. Classic examples include when a new population starts from a few individuals (founder effect) or when a population experiences a sharp decline (bottleneck effect). This differs from natural selection, where alleles spread because they increase reproductive success, from nonrandom mating, which changes genotype frequencies through biased pairing, and from gene flow, which changes frequencies by introducing alleles from other populations.