Selection coefficient

Selection coefficient, usually denoted by the letter s, is a measure used in population genetics to quantify the relative fitness of a genotype compared to other genotypes. Selection coefficients are central to the quantitative description of evolution, since fitness differences determine the change in genotype frequencies attributable to selection.

The selection coefficient is typically calculated using fitness values. The fitness ( $W$ ) of a genotype is a measure of its reproductive success, often expressed as a fraction of the maximum reproductive success in the population. The formula to calculate the selection coefficient $s$ for a genotype is: $s=1-W$ , where $W$ is the relative fitness of the genotype, ranging between 0 and 1.^[1]^[2]

Suppose we have two genotypes, $AA$ and $Aa$ , with relative fitness values of 1 (most fit, standard reference) and 0.8, the selection coefficient ( $s$ ) for $AA$ is $1-1=0$ (no selection against this genotype); the selection coefficient ( $s$ ) for $Aa$ is $1-0.8=0.2$ (this indicates that the $Aa$ genotype has 20% reduction in fitness compared to the $AA$ genotype).

For example, the lactose-tolerant allele spread from very low frequencies to high frequencies in less than 9000 years since farming with an estimated selection coefficient of 0.09-0.19 for a Scandinavian population. Though this selection coefficient might seem like a very small number, over evolutionary time, the favored alleles accumulate in the population and become more and more common, potentially reaching fixation.^[3]

References

^ "Selection Coefficient". Encyclopedia of Genetics, Genomics, Proteomics and Informatics. Springer. 16 July 2016. p. 1775. doi:10.1007/978-1-4020-6754-9_15281. ISBN 978-1-4020-6754-9.
^ Gillespie, John H. (2004). Population genetics : a concise guide (2nd ed.). Baltimore, Md.: Johns Hopkins University Press. ISBN 0801880092.
^ Bersaglieri, T. et al. Genetic signatures of strong recent positive selection at the lactase gene. Am. J. Hum. Genet. 74,1111-1120(2004).

[1] "Selection Coefficient". Encyclopedia of Genetics, Genomics, Proteomics and Informatics. Springer. 16 July 2016. p. 1775. doi:10.1007/978-1-4020-6754-9_15281. ISBN 978-1-4020-6754-9.

[2] Gillespie, John H. (2004). Population genetics : a concise guide (2nd ed.). Baltimore, Md.: Johns Hopkins University Press. ISBN 0801880092.

[3] Bersaglieri, T. et al. Genetic signatures of strong recent positive selection at the lactase gene. Am. J. Hum. Genet. 74,1111-1120(2004).

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v t e Population genetics
Key concepts	Hardy–Weinberg principle Genetic linkage Identity by descent Linkage disequilibrium Fisher's fundamental theorem Neutral theory Shifting balance theory Price equation Coefficient of inbreeding Coefficient of relationship Selection coefficient Fitness Heritability Population structure Constructive neutral evolution
Selection	Natural Artificial Sexual Ecological
Effects of selection on genomic variation	Genetic hitchhiking Background selection
Genetic drift	Small population size Population bottleneck Founder effect Coalescence Balding–Nichols model
Founders	R. A. Fisher J. B. S. Haldane Sewall Wright
Related topics	Biogeography Evolution Evolutionary game theory Fitness landscape Genetic genealogy Landscape genetics and genomics Microevolution Population genomics Phylogeography Quantitative genetics
Index of evolutionary biology articles

See also

References