Gene Frequency Definition

Correct Answer: Gene Frequency

Gene frequency (allele frequency) is the fraction of all alleles at a given locus in a specified population that are of a particular type. According to Hardy-Weinberg equilibrium, for a two-allele system: p + q = 1.

Hardy-Weinberg Law (Table 8 from notes)

• In a large, random-mating population, in the absence of mutation, migration and selection — gene and genotypic frequencies remain constant from generation to generation.
• Gene frequencies: p (for A), q (for a); where p + q = 1
• Genotypic frequencies: P (AA) = p², H (Aa) = 2pq, Q (aa) = q²; where P + H + Q = 1
• Gene frequency from genotypic frequency: p = P + ½H; q = Q + ½H

Key Note

Frequency of heterozygotes (2pq) cannot exceed 50% and is maximum when p = q = 0.5

Why Other Options Are Wrong

• Genotypic frequency: Proportion of a specific genotype (AA, Aa, aa) — different from allele frequency.
• Phenotypic frequency: Proportion of individuals showing a particular phenotype — includes environmental effects.
• Allelic diversity: Not a standard genetics term for this concept.