Which factor can lead to gene drift in a population?

Population bottlenecks are significant events that drastically reduce the size of a population, leading to a loss of genetic diversity. When a population undergoes a bottleneck, only a small number of individuals contribute genetically to the next generation. This can result in gene drift, where the genetic composition of the surviving population can change significantly over time due to the limited genetic variation. The genes of the few individuals that survive become more common in the population, possibly leading to the fixation or loss of certain alleles purely by chance, rather than by natural selection.

In contrast, random mating and gene flow between populations do not inherently lead to gene drift. Random mating helps maintain genetic variation and can reduce genetic differences within a population. Gene flow introduces new alleles into a population from another population, which can increase diversity rather than decrease it. Genetic mutations can introduce new alleles but do not cause gene drift on their own; instead, gene drift results from stochastic changes in allele frequencies due to population size reductions or random sampling effects. Therefore, population bottlenecks are primarily responsible for leading to gene drift in a population through the mechanisms of reduced genetic diversity and increased random fluctuations in allele frequencies.