Allele Frequency Calculator
Enter how many individuals have each genotype (AA, Aa, aa) to compute the allele frequencies p and q.
Allele frequencies are found by counting alleles across a population. Each individual has two alleles, so p (dominant) = (2 × AA + Aa) ÷ 2N and q (recessive) = (2 × aa + Aa) ÷ 2N, where N is the total. For 30 AA, 60 Aa and 10 aa, p = 120 ÷ 200 = 0.6 and q = 80 ÷ 200 = 0.4.
How to Use This Calculator
Enter the number of individuals in each of the three genotype classes: homozygous dominant (AA), heterozygous (Aa), and homozygous recessive (aa). The calculator counts up all the alleles in the population and returns the frequency of the dominant allele (p) and the recessive allele (q).
This is the direct, count-based way to find allele frequencies when you have genotype data — no assumptions about equilibrium are needed. Once you have p and q, you can compare the population against Hardy-Weinberg expectations to test whether it is evolving.
How the Calculation Works
Every individual carries two copies of the gene, so a population of N individuals has 2N alleles in total. Each AA individual contributes two dominant alleles, each Aa contributes one dominant and one recessive, and each aa contributes two recessive. The dominant allele frequency is therefore p = (2 × AA + Aa) ÷ 2N, and the recessive frequency is q = (2 × aa + Aa) ÷ 2N. Since every allele is either dominant or recessive, p + q always equals 1.
Worked Example
A population has 30 AA, 60 Aa and 10 aa individuals, so N = 100 and there are 200 alleles. Dominant alleles = 2 × 30 + 60 = 120, giving p = 120 ÷ 200 = 0.6. Recessive alleles = 2 × 10 + 60 = 80, giving q = 80 ÷ 200 = 0.4. Check: p + q = 0.6 + 0.4 = 1.0. So the dominant allele makes up 60% of the gene pool and the recessive 40%.
What the Result Means
The allele frequencies describe the makeup of the population's gene pool — the raw material on which evolution acts. Tracking how p and q change over generations is the most direct way to detect evolution in action; a shift in allele frequency is, by definition, evolution at that locus. You can also feed these frequencies into the Hardy-Weinberg equation to predict the genotype frequencies you would expect under equilibrium, then compare them to your observed counts to see whether some evolutionary force is at play.
Assumptions and Limitations
This calculation is exact and assumption-free for the counts you provide — it is simply careful counting. Its accuracy depends on correctly classifying genotypes, which requires that heterozygotes can be distinguished (through codominance, molecular markers or test crosses); if dominant homozygotes and heterozygotes look identical, you cannot separate AA from Aa by phenotype alone and would need the Hardy-Weinberg approach instead. It covers a single gene with two alleles.
When to Use an Allele Frequency Calculator
Genetics students use this to compute allele frequencies p and q directly from genotype counts. Run it to analyze a population sample, complete population-genetics homework, or set up a comparison against Hardy-Weinberg expectations. Enter the counts of each genotype to get the allele frequencies.
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Open calculator →Frequently Asked Questions
How do I calculate allele frequency from genotype counts?
Count the alleles: p = (2 × number of AA + number of Aa) ÷ 2N, and q = (2 × number of aa + number of Aa) ÷ 2N, where N is the total number of individuals.
Why do I multiply by 2?
Because each individual carries two alleles of the gene. A population of N individuals has 2N alleles, and each homozygote contributes two of the same allele.
What is the difference between allele and genotype frequency?
Allele frequency is the proportion of each allele in the gene pool (p and q). Genotype frequency is the proportion of individuals with each genotype (AA, Aa, aa). Allele frequencies are computed from genotype counts.
Should p and q add up to 1?
Yes, always, for a gene with two alleles. Every allele is either dominant or recessive, so their frequencies together account for the entire gene pool and must sum to 1.
Do I need Hardy-Weinberg to find allele frequencies?
No. If you have genotype counts, you count alleles directly with no assumptions. Hardy-Weinberg is only needed when you cannot distinguish heterozygotes from dominant homozygotes.
What if I only know the phenotype counts?
If heterozygotes are indistinguishable from dominant homozygotes, you cannot count alleles directly. Instead, use the recessive phenotype frequency as q² and take the square root to estimate q under Hardy-Weinberg.
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