Which statement best describes how natural selection affects allele frequencies?

• A. Differential fitness changes allele frequencies by changing genotype fitness values w_AA, w_Aa, w_aa.
• B. Selection increases recombination rate.
• C. Selection reduces mutation rate.
• D. Selection has no effect on allele frequencies.

Answer: (C)

Natural selection shifts allele frequencies because different genotypes contribute different numbers of offspring to the next generation. Each genotype has a fitness value (w_AA, w_Aa, w_aa) that determines its reproductive success. When some genotypes are fitter, the alleles they carry become more common over time, since those alleles are passed on more frequently to future generations. The changes in allele frequency arise from how the average fitness of the population weights the contribution of each genotype, not from altering mutation or recombination rates. So the correct idea is that differential fitness changes allele frequencies by the genotype fitness values that selection acts upon.