F-Statistics Calculator (Fst, Fis, Fit)

F-statistics measure how genetic variation is distributed within and between populations — a core concept in evolutionary biology and population genetics. Enter the counts of AA, Aa, and aa genotypes for 2 or 3 populations into the F-Statistics Calculator to calculate Fst (population differentiation), Fis (inbreeding coefficient), and Fit (overall fixation index). Select the number of populations and fill in each group's genotype counts to see all three F-statistics along with the total number of individuals.

Results

Fst (Population Differentiation)

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Fis (Inbreeding Coefficient)

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Fit (Overall Fixation Index)

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Total Individuals

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Results Table

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Frequently Asked Questions

What do Fst, Fis, and Fit measure in population genetics?

Fst measures population differentiation (genetic distance between populations), Fis measures inbreeding within populations (deviation from Hardy-Weinberg equilibrium), and Fit measures overall fixation index (combined effect of population structure and inbreeding).

How do I interpret F-statistic values?

F-statistics range from -1 to +1. Positive values indicate reduction in heterozygosity (inbreeding or population structure), zero indicates random mating, and negative values indicate excess heterozygosity (heterozygote advantage or population mixing).

What does a high Fst value indicate?

A high Fst value (approaching 1) indicates strong population differentiation, meaning the populations are genetically distinct. Low Fst values (near 0) suggest little genetic difference between populations.

How is allele frequency calculated from genotype counts?

Allele frequency is calculated as: frequency of A = (2 × AA + Aa) / (2 × total individuals). Each homozygote contributes two alleles, each heterozygote contributes one allele of each type.

What is the relationship between Fst, Fis, and Fit?

The three F-statistics are related by the equation: (1 - Fit) = (1 - Fis)(1 - Fst). This shows how overall fixation index combines the effects of inbreeding and population structure.

When should I use F-statistics in population genetics?

F-statistics are useful for analyzing population structure, measuring genetic diversity, detecting inbreeding, studying gene flow between populations, and understanding evolutionary processes in natural and managed populations.

What sample sizes do I need for reliable F-statistic calculations?

Larger sample sizes provide more reliable estimates. Generally, at least 25-50 individuals per population are recommended, though this depends on the allele frequencies and the precision required for your study.