How does population size affect the likelihood of changes in allele frequencies by chance alone?

Answer 1

Mutation rates are small but constant. With a typical mutation rate of 1 x 10-6, it is expected that 1 out of a million individuals in a population will carry the mutation. If the population size is small (10,000 or fewer individuals), the probability that the mutation will be present is small (~1% with 104 individuals). If population sizes are large (107 or more individuals), the probability that the mutation will be present is large (~10 mutants expected if 107 individuals are in the population). Mutations can be lost from populations through genetic drift, and large populations experience less genetic drift than small populations. Thus mutations are more likely to exist and persist in large populations than in small populations.

Answer 2

In smaller populations, chance events like genetic drift can have a greater impact on allele frequencies, leading to more rapid changes in the genetic makeup of the population. In larger populations, random fluctuations have less influence on allele frequencies because there is more genetic diversity and a larger gene pool to buffer against these changes.