population genetics Population genetics is a subfield of genetics that deals with genetic differences within and between populations, and is a part of evolutionary biology. Studies in this branch of biology examine such phenomena as adaptation, speciation, and po ...

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

selection Selection may refer to: Science * Selection (biology), also called natural selection, selection in evolution ** Sex selection, in genetics ** Mate selection, in mating ** Sexual selection in humans, in human sexuality ** Human mating strateg ...

. The following definition of ''s'' is commonly used. Suppose that there are two genotypes ''A'' and ''B'' in a population with relative fitnesses

w_A

and

w_B

respectively. Then, choosing genotype ''A'' as our point of reference, we have

w_A=1

, and

w_B=1+s

, where ''s'' measures the fitness advantage (''s''>0) or disadvantage (''s''<0) of ''B''. 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.Bersaglieri, T. et al. Genetic signatures of strong recent positive selection at the lactase gene. Am. J. Hum. Genet. 74,1111-1120(2004).

References

{{Population genetics Population genetics Evolutionary biology

See also

References