Allele Frequency Calculator
Enter the number of homozygous dominant, heterozygous and homozygous recessive individuals, and this calculator counts alleles to find the A and a frequencies.
How to find allele frequencies
- Count the individuals of each genotype: AA, Aa and aa.
- Enter those three counts.
- Read the dominant (A) and recessive (a) allele frequencies, which sum to 1.
Examples
Mixed population
AA = 320, Aa = 160, aa = 20
freqA = 0.8, freqa = 0.2 (total 500)
Even split
AA = 25, Aa = 50, aa = 25
freqA = 0.5, freqa = 0.5 (total 100)
Frequently asked questions
How do you calculate allele frequency from genotype counts?
Count alleles. The A count is 2 times the AA count plus the Aa count. Divide by the total allele pool, which is 2 times the number of individuals.
Why multiply the total by two?
Each individual is diploid and carries two alleles at the locus, so a population of N individuals holds 2N alleles. Frequencies use that total as the denominator.
Do the two frequencies have to add up to one?
Yes. With only two alleles, the A frequency plus the a frequency always equals 1, since every allele in the pool is either A or a.
Is this the same as the Hardy-Weinberg calculation?
This step counts observed alleles. Hardy-Weinberg then predicts expected genotype frequencies from those allele frequencies, assuming an idealized population.
What if I only know phenotype counts?
You cannot split dominant phenotypes into AA and Aa from counts alone. You need genotype counts, or you must assume Hardy-Weinberg equilibrium to estimate them.
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