Allele Frequency Calculator

Allele frequency (gene frequency) is the proportion of a specific allele among all copies of that gene in a population. For diploid organisms: Frequency = (Number of that allele) / (Total alleles). Example: In 100 people (200 alleles), if 60 are allele A and 140 are allele a, then p(A) = 60/200 = 0.3 (30%), q(a) = 140/200 = 0.7 (70%). Always: p + q = 1.

Hardy-Weinberg equation: p² + 2pq + q² = 1, where p = frequency of dominant allele (A), q = frequency of recessive allele (a), p² = frequency of AA, 2pq = frequency of Aa, q² = frequency of aa. Predicts genotype frequencies in populations under no evolution (no mutation, migration, selection, genetic drift, random mating).

For recessive diseases: (1) Disease prevalence = q² (affected individuals), (2) q = √(prevalence), (3) p = 1 - q, (4) Carrier frequency = 2pq. Example: Cystic fibrosis affects 1/2500 = 0.0004. q² = 0.0004, q = 0.02, p = 0.98, carrier frequency = 2(0.98)(0.02) = 0.0392 or 3.92% (1 in 25 carriers).

Deviation from HW equilibrium indicates evolutionary forces acting on population: Natural selection (favoring/against alleles), Mutation (creating new alleles), Migration (gene flow between populations), Genetic drift (random changes, especially small populations), Non-random mating (inbreeding, assortative mating). Chi-square test (χ² > 3.841) suggests significant deviation. HW is theoretical baseline for comparison.

Difficult for dominant diseases because: (1) Affected individuals = p² + 2pq (two genotypes), (2) Cannot distinguish AA from Aa phenotypically, (3) Many dominant disorders have incomplete penetrance or variable expression. Better for: Recessive disorders (q² = affected, easily measured), calculating risk for genetic counseling, population screening programs. Use pedigree analysis for dominant disorders.