Allele Frequency Calculator
From Genotype Counts to Population-Level Allele Frequencies
A single organism has a genotype; a population has allele frequencies. Counting how many individuals in a sample are homozygous dominant, heterozygous, and homozygous recessive lets you work backward to the proportion of each allele circulating in the gene pool — the basic input for almost every downstream population genetics calculation, including Hardy-Weinberg analysis.
The Formula
q = 1 − p
Each AA individual contributes two copies of the A allele and each Aa individual contributes one, out of two allele copies per individual overall — so the total count of A alleles divided by the total allele count (twice the population size) gives p, the frequency of the A allele. q, the frequency of the alternate allele, is whatever's left.
Worked Example
A sample of 100 individuals: 40 AA, 40 Aa, 20 aa.
| Allele | Frequency |
|---|---|
| p (A) | 0.6000 |
| q (a) | 0.4000 |
Why This Matters
- Conservation genetics — tracking allele frequency shifts across generations in a monitored wildlife population can flag inbreeding depression or genetic drift before it threatens viability.
- Agricultural breeding — measuring how a desirable allele's frequency changes under selective breeding pressure in livestock or crop lines.
- Population genetics coursework — the standard first step before testing a population against Hardy-Weinberg equilibrium expectations.
How to Use This Calculator
- Enter the number of individuals with the AA (homozygous dominant) genotype.
- Enter the number with the Aa (heterozygous) genotype.
- Enter the number with the aa (homozygous recessive) genotype.
- Select Calculate to get the p and q allele frequencies for the sample.
Related Calculations
Feed these frequencies into the Hardy-Weinberg Calculator to test for equilibrium, or compare against the Heterozygosity Calculator for observed versus expected heterozygosity.