Genetic drift

Genetic drift is random change in allele frequency caused by finite-population sampling.

Even when two alleles have identical fitness, their frequencies need not remain constant from one generation to the next.

Fixation and loss

In a finite population without mutation, an allele may eventually reach frequency \(1\) and become fixed, or frequency \(0\) and be lost.

Population size

Random fluctuations are generally stronger in smaller populations. Thus deterministic allele-frequency equations can miss an important mechanism when population size is limited.