Fixation index

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See FST for other meanings of Fst

Fixation index (FST) is a measure of population differentiation based on genetic polymorphism data (either SNPs or microsatellites). It is a special case of F-statistics, concept developed in the 1920s by Sewall Wright.

This statistic compares the genetic variability within and between population and is frequently used in the field of population genetics.

Several definitions of Fst have been used, all measuring different but related quantities. A common definition has been proposed by Hudson, Slatkin and Maddison (1992):

F_{ST} = \frac{ \Pi_{Between} - \Pi_{Within} } { \Pi_{Between} }

where ΠBetween and ΠWithin represent the average number of pairwise differences between two individuals sampled from different (ΠBetween) or the same (ΠWithin) population. Note that when using this definition ΠWithin should be computed for each population and then averaged. Otherwise, random sampling of pairs within populations put all the weight on the population with the largest sample size.


[edit] References

Estimation of levels of gene flow from DNA sequence data, R. R. Hudson and M. Slatkin and W. P. Maddison, Genetics 1992

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