Calculator
Use observed genotype counts or direct allele frequencies.
Example Data Table
This example shows observed and expected values for a sample population.
| Population | AA Count | Aa Count | aa Count | Allele p | Allele q | Expected Aa Frequency |
|---|---|---|---|---|---|---|
| Study Group 1 | 36 | 48 | 16 | 0.60 | 0.40 | 0.48 |
| Study Group 2 | 49 | 42 | 9 | 0.70 | 0.30 | 0.42 |
| Study Group 3 | 25 | 50 | 25 | 0.50 | 0.50 | 0.50 |
Formula Used
Observed genotype frequencies
f(AA) = n(AA) / N
f(Aa) = n(Aa) / N
f(aa) = n(aa) / N
Allele frequencies
p = [2n(AA) + n(Aa)] / 2N
q = [2n(aa) + n(Aa)] / 2N = 1 - p
Hardy-Weinberg expectations
Expected frequency of AA = p²
Expected frequency of Aa = 2pq
Expected frequency of aa = q²
Additional measures
Expected count = expected frequency × sample size
χ² = Σ (Observed - Expected)² / Expected
Fixation index F = 1 - (Observed heterozygosity / Expected heterozygosity)
How to Use This Calculator
- Enter a population label and optional allele symbols.
- Select either observed genotype counts or allele frequency input.
- Fill the visible fields with your study values.
- Choose the number of decimal places for reporting.
- Press the calculate button to show results above the form.
- Review genotype frequencies, expected counts, carrier rates, and fit statistics.
- Use the CSV or PDF buttons to export the displayed output.
FAQs
1. What does this genotype frequency calculator do?
It calculates observed genotype frequencies, allele frequencies, expected Hardy-Weinberg frequencies, expected counts, carrier rates, heterozygosity, and a chi-square fit measure when observed counts are supplied.
2. What is genotype frequency?
Genotype frequency is the proportion of individuals carrying a specific genotype in a population. You find it by dividing the count of that genotype by the total number of individuals.
3. What are p and q in population genetics?
p is the frequency of one allele, and q is the frequency of the alternate allele. For a two-allele system, p + q must equal 1.
4. Why are expected frequencies based on p², 2pq, and q²?
Under Hardy-Weinberg assumptions, random mating and stable allele frequencies produce expected genotype proportions of p² for homozygous dominant, 2pq for heterozygous, and q² for homozygous recessive.
5. What does the chi-square value mean here?
It summarizes how far observed genotype counts differ from expected counts. Smaller values suggest closer agreement. Interpretation still depends on assumptions, sample design, and the chosen significance level.
6. What is expected heterozygosity?
Expected heterozygosity is the predicted heterozygous frequency under Hardy-Weinberg equilibrium. For two alleles, it equals 2pq and reflects genetic variation within the population.
7. What is the fixation index F?
The fixation index compares observed heterozygosity with expected heterozygosity. Positive values suggest fewer heterozygotes than expected, while negative values suggest more heterozygotes than expected.
8. Can I use this for any species?
Yes, for any diploid organism with a two-allele locus. The interpretation is strongest when sampling is representative and Hardy-Weinberg assumptions are reasonable for the studied population.