Allele Frequency Calculator
Calculate allele frequencies from genotype counts or observed phenotypes. Find dominant and recessive allele frequencies for any locus in a diploid population.
🧬 Genetics📐 p = (2N_AA + N_Aa) / 2N🧬 Biology
Number of AA homozygotes
Number of Aa heterozygotes
Number of aa homozygotes
Total population N (auto-calculated)
Please enter valid values.
Formula & Reference
| Variable | Symbol | Formula | Units |
|---|---|---|---|
| Allele Frequency Calculator | — | p = (2N_AA + N_Aa) / 2N | frequency |
Step-by-Step Examples
Example 1
Blood Type MN
490 MM, 420 MN, 90 NN in a population of 1000.
- p(M) = (2x490 + 420)/(2x1000) = 1400/2000 = 0.70
- q(N) = (2x90 + 420)/2000 = 600/2000 = 0.30
- Check: p + q = 0.70 + 0.30 = 1.00 ✓
✓ p(M) = 0.70, q(N) = 0.30
Example 2
From Phenotype Counts
In a population of 1000: 160 albinos (aa), 840 normal. Find q.
- q² = 160/1000 = 0.16
- q = sqrt(0.16) = 0.40
- p = 1 - 0.40 = 0.60
- Carrier (Aa): 2 x 0.60 x 0.40 = 0.48 = 48%
✓ q = 0.40, p = 0.60 (assuming H-W)
Example 3
Three-Allele System
Locus with alleles A1 (frequency f1), A2, A3. Count: 200 A1A1, 300 A1A2, 100 A2A2, 400 A1A3. N=1000.
- 2N = 2000 total alleles
- p(A1) = (2x200+300+400)/2000 = 1100/2000 = 0.55
- p(A2) = (2x100+300)/2000 = 500/2000 = 0.25
- p(A3) = 400/2000 = 0.20
✓ p(A1)=0.55, p(A2)=0.25, p(A3)=0.20
Real-World Applications
Conservation Genetics
Monitor allele frequencies over generations in endangered species to track genetic diversity loss.
Medical Genetics
Drug response variants: allele frequencies determine population-level pharmacogenomics impact.
Evolution Research
Allele frequency change over time is the fundamental measure of microevolution.
Forensic DNA
Allele frequencies used to calculate match probabilities in DNA evidence.
Common Mistakes to Avoid
⚠️
Count alleles, not individuals
p = (2 x AA + Aa) / (2N). Each individual contributes 2 alleles. A heterozygote contributes one of each.
⚠️
Frequencies must sum to 1
For 2 alleles: p + q = 1. For 3 alleles: p + q + r = 1. Always verify your calculation sums correctly.
⚠️
H-W assumption required for phenotype method
Using q² = frequency of recessives to find q assumes Hardy-Weinberg equilibrium. If not in H-W, must count genotypes directly.
Frequently Asked Questions
What is an allele frequency? ▾
The proportion of a specific allele among all alleles at that locus in the population. Ranges from 0 (absent) to 1 (fixed).
How do I find allele frequency from genotype data? ▾
Count alleles directly: p = (2*n_AA + n_Aa) / (2*N). More accurate than using phenotype frequencies.
What is allele fixation? ▾
When p = 1.0 or q = 1.0: one allele is fixed (the other is lost). Common end-state for genetic drift in small populations.
Can I measure allele frequency change? ▾
Yes. Allele frequency change per generation (delta-p) measures strength of selection or drift. Compare frequencies across generations.
What determines allele frequency in nature? ▾
Mutation (introduces new alleles), genetic drift (random change in small populations), natural selection (favors adaptive alleles), gene flow (migration mixes populations).