Allele Frequency Calculator
Allele frequency calculator using the Hardy-Weinberg equilibrium equation. Compute carrier probability and genotype frequencies from disease prevalence for recessive traits.
About This Calculator
The Allele Frequency Calculator uses the Hardy-Weinberg equilibrium equation to compute allele and genotype frequencies from disease prevalence data. It is designed for students, genetic counselors, healthcare professionals, and anyone curious about their carrier probability for autosomal recessive genetic disorders.
How It Works
The Hardy-Weinberg principle states that in a large, randomly mating population with no evolutionary forces, allele and genotype frequencies remain constant across generations. For a gene with two alleles (dominant A and recessive a), the relationship is expressed as:
p + q = 1 and p² + 2pq + q² = 1
Where p is the frequency of the healthy allele, q is the frequency of the mutant allele, p² represents homozygous dominant individuals, 2pq represents carriers (heterozygous), and q² represents affected individuals (homozygous recessive). Given the prevalence q² of a recessive disease, the calculator finds q = √(q²), then p = 1 - q, and derives all genotype frequencies.
Regional Notes
Disease prevalence varies significantly across populations and geographic regions. For example, cystic fibrosis has a carrier frequency of approximately 1 in 25 in Caucasian populations of Northern European descent, while Tay-Sachs disease is more common in Ashkenazi Jewish populations (carrier frequency ~1 in 27). Sickle cell anemia carrier frequency reaches 1 in 12 in African-American populations but is rare in most other groups. Always use prevalence data specific to the relevant ethnic and geographic population when assessing carrier risk. Genetic counseling should be sought for personalized risk assessment.
Frequently Asked Questions
What is the Hardy-Weinberg equilibrium equation?
The Hardy-Weinberg equilibrium equation is p² + 2pq + q² = 1, where p is the frequency of the dominant (healthy) allele, q is the frequency of the recessive (mutant) allele, p² is the frequency of homozygous dominant individuals, 2pq is the frequency of carriers (heterozygous), and q² is the frequency of affected individuals (homozygous recessive). The equation assumes a large, randomly mating population with no mutation, migration, or selection.
How do I use the Allele Frequency Calculator?
Enter the disease frequency either as a proportion (1 in X people are affected) or as a percentage (q²%). You can also select a preset disease from the dropdown. Click Calculate to see the healthy and mutant allele frequencies, genotype frequencies, and your carrier probability — the chance that you carry one copy of the mutant allele.
What does carrier probability mean?
Carrier probability (1 in X) is the chance that a randomly selected individual from the population carries one copy of the mutant allele. Carriers have one healthy and one impaired gene — they typically do not show symptoms but can pass the mutation to their children. If both parents are carriers of the same recessive disease, each child has a 25% chance of being affected.
Is this calculator free to use?
Yes, the Allele Frequency Calculator is completely free to use with no registration or login required. You can share your results by copying the URL, which saves all your input values automatically.
What is the difference between allele frequency and genotype frequency?
Allele frequency (p or q) measures how common a specific gene variant is in the population. Genotype frequency (p², 2pq, q²) measures how common each genetic combination is. For example, if q = 0.01, the mutant allele appears in 1% of all gene copies, but only 0.01% of people (q² = 0.0001) actually have two copies and are affected by the disease.
How do you calculate allele frequency from disease prevalence?
For an autosomal recessive disease, the affected frequency q² equals the disease prevalence. To find q (mutant allele frequency), take the square root of q². Then p (healthy allele frequency) = 1 - q. For example, if a disease affects 1 in 2,500 people, q² = 1/2500 = 0.0004, q = sqrt(0.0004) = 0.02, and p = 0.98.
Can I use this calculator for any population?
Yes, the Hardy-Weinberg equation applies to any large population with random mating. However, different ethnic and geographic populations have different allele frequencies for the same disease. For example, cystic fibrosis affects 1 in 2,500 Caucasians but is rarer in Asian populations. Always use disease prevalence data specific to the relevant population for accurate results.
What assumptions does the Hardy-Weinberg equilibrium make?
The Hardy-Weinberg equilibrium assumes: (1) a very large population size (no genetic drift), (2) random mating, (3) no mutation, (4) no migration (gene flow), and (5) no natural selection. In reality, populations rarely meet all these conditions, but the model provides a useful baseline for comparing observed genetic variation against expected frequencies.