Selection Coefficient Calculator

In population genetics, the selection coefficient measures how strongly natural selection acts against (or in favor of) a particular genotype relative to the fittest type. Enter the fitness values for all three genotypes (AA, Aa, and aa), an initial allele frequency (p), and a number of generations into the Selection Coefficient Calculator to get the Selection Coefficient (s) and Dominance Coefficient (h). Secondary outputs include relative fitness for each genotype and the projected final allele frequency after your chosen generations.

Usually set to 1.0 as the reference fitness

Can be higher than 1.0 for overdominance

Frequency of the A allele (0 to 1)

Number of generations to simulate

Results

Selection Coefficient (s)

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Dominance Coefficient (h)

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Relative Fitness (AA)

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Relative Fitness (Aa)

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Relative Fitness (aa)

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Final Allele Frequency

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Results Table

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Frequently Asked Questions

What is a selection coefficient?

A selection coefficient (s) measures the relative reduction in fitness of a genotype compared to the most fit genotype in the population. It ranges from 0 (no selection) to 1 (lethal), with s = 1 - W, where W is the relative fitness.

How do you calculate relative fitness?

Relative fitness is calculated by dividing each genotype's absolute fitness by the highest fitness value among all genotypes. The most fit genotype has a relative fitness of 1.0, while others have values between 0 and 1.

What does the dominance coefficient represent?

The dominance coefficient (h) determines how the heterozygote fitness relates to the homozygotes. h = 0 means complete dominance, h = 0.5 means additive effects, and h = 1 means the recessive allele is completely recessive.

What are the different types of natural selection?

Natural selection can be directional (favoring one extreme), balancing (maintaining multiple alleles), or disruptive (favoring extremes over intermediates). The selection coefficient helps quantify the strength of these selective forces.

How does selection affect allele frequencies over time?

Selection changes allele frequencies each generation. Positive selection increases beneficial allele frequencies, while negative selection decreases harmful allele frequencies. The rate depends on the selection coefficient and dominance relationships.

What is considered strong vs. weak selection?

Selection coefficients above 0.1 are generally considered strong, while those below 0.01 are weak. Most natural selection is relatively weak (s < 0.05), but even small coefficients can have significant evolutionary effects over many generations.

Can fitness values be greater than 1?

Yes, fitness values can exceed 1.0 when a genotype has higher survival or reproductive success than the reference. This commonly occurs with heterozygote advantage (overdominance) where the heterozygote is most fit.