0.4
0.36
0.48
0.16
0.84
0.16
0.48
0.52
1
0.4
0.36
0.48
0.16
0.84
0.16
0.48
0.52
1
The Genotype Frequency Calculator predicts the expected genotype frequencies in a population under Hardy-Weinberg equilibrium given a known allele frequency. This is the forward calculation: from allele frequencies to expected genotype proportions, which is essential for predicting genetic composition in populations.
Enter the frequency of the dominant allele (p), and the calculator will compute q and all three genotype frequencies (AA, Aa, aa).
Under Hardy-Weinberg equilibrium, genotype frequencies are predicted from allele frequencies:
Frequency of AA = p²
Frequency of Aa = 2pq
Frequency of aa = q²
Where q = 1 − p. These frequencies always sum to 1: p² + 2pq + q² = 1 (which is the binomial expansion of (p + q)²).
Inputs
Results
With p=0.6 and q=0.4: 36% AA, 48% Aa (heterozygous), and 16% aa. Heterozygotes are the most common genotype.
Inputs
Results
When the dominant allele is rare (p=0.1): only 1% are homozygous dominant, 18% are carriers, and 81% are homozygous recessive.
The heterozygote frequency (2pq) is maximized when p = q = 0.5, giving 2pq = 0.5. This is because heterozygotes carry one of each allele, so they are most likely when both alleles are equally common. The formula 2pq always produces a maximum at p = 0.5 for a two-allele system.
If you can identify homozygous recessives by phenotype, their frequency equals q². Take the square root to get q, then p = 1 − q. For codominant alleles where all genotypes are distinguishable, use the allele counting method directly from genotype counts.
The Hardy-Weinberg principle extends to multiple alleles. For three alleles (p, q, r), the expansion is (p + q + r)² = p² + q² + r² + 2pq + 2pr + 2qr = 1. This calculator handles the two-allele case. For multi-allele systems, each additional allele adds more genotype classes.
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