In finite populations, how do mutation and genetic drift interact to influence allele frequencies?

• A. Drift causes random fluctuations; mutation introduces new alleles at rate μ, creating a balance.
• B. Drift creates new alleles; mutation fixes them.
• C. Drift causes mutation to disappear.
• D. Mutation eliminates drift.

Answer: (A)

In finite populations, allele frequencies are shaped by two forces that interact: genetic drift, which is random sampling from generation to generation and causes allele frequencies to wander, sometimes leading to fixation or loss; and mutation, which continuously introduces new alleles at a small rate μ. Because drift tends to erode variation while mutation keeps injecting new variants, the two balance out over time, leading to a mutation–drift balance. This explains why allele frequencies exhibit random fluctuations but are replenished by new alleles entering the population. The idea that drift creates new alleles isn’t accurate—drift acts on existing variation—while mutation is the source of new alleles, and drift can still fix or lose them despite mutation’s input.