McDonald–Kreitman test

The McDonald-Kreitman Test looks for ancient selection over long periods, and is based on divergence between related species. It was first devised by John McDonald and Martin Kreitman in 1991, based on an investigation of differences in amino acid sequence of the alcohol dehydrogenase gene of Drosophila species.^[1]

	Fixed	Polymorphic
Synonymous	D_s	P_s
Nonsynonymous	D_n	P_n

Sites are classed as polymorphic if they show any variation within species, while they are classed as fixed if they differ between species but not within them. If the ratio of fixed differences to polymorphisms is much higher for nonsynonymous changes (i.e. D_n/P_n >> D_s/P_s), this indicates that genetic changes have been subject to positive selection.^[2]

^ http://www.nature.com/nature/journal/v351/n6328/abs/351652a0.html
^ N.H. Barton, D.E.G. Briggs, J.A. Eisen, D.B. Goldstein, N.H. Patel. Evolution. Cold Spring Harbor. Woodbury, NY. 2007

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[1] ttp://www.nature.com/nature/journal/v351/n6328/abs/351652a0.html

[2] N.H. Barton, D.E.G. Briggs, J.A. Eisen, D.B. Goldstein, N.H. Patel. Evolution. Cold Spring Harbor. Woodbury, NY. 2007

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