Which statement best defines allele frequency and its change over time?

• A. Allele frequency is the speed at which genes are transcribed.
• B. Allele frequency is the total number of individuals in a population.
• C. Allele frequency is the number of alleles replaced during mutation.
• D. Allele frequency is the proportion of a given allele in a population; it changes via mutation, selection, gene flow, genetic drift, and nonrandom mating.

Answer: (D)

Allele frequency is the proportion of a specific allele among all copies of that gene in a population. For a gene with two alleles, those frequencies add up to 1 (p + q = 1), describing how common each allele is in the gene pool. This frequency can change across generations because evolution acts through several processes: mutation introduces new alleles and can alter frequencies; natural selection changes how common alleles are based on fitness; gene flow (migration) adds or removes alleles when individuals move between populations; genetic drift causes random fluctuations in allele frequencies, especially in small populations; and nonrandom mating affects how often particular alleles appear together in individuals, which can shift allele frequencies over time in certain contexts. So the best definition is that allele frequency is the proportion of a given allele in a population, and it changes due to those evolutionary forces.