title: Estimating selection by comparing synonymous and substitutional changes.
abstract: A higher ratio of substitutional to synonymous changes in between-species than in within-species comparisons has been taken as evidence for positive selection changing amino acids. A model is presented in which a difference of this kind arises as a result of purely neutral mutations, provided that the "species" compared are sufficiently different to approach a steady state between forward and backward mutation. In Neisseria, substitutions are twice as frequent, relative to synonymous changes, in between-species comparisons: it is shown that the data are consistent with the neutral model. The argument does not invalidate evidence for positive selection, for example in Drosophila, when the species compared are fairly similar.
authors.affiliation: School of Biological Sciences, University of Sussex, Brighton, United Kingdom.
authors.forename: J M
authors.initials: JM
authors.lastname: Smith
mesh_terms: D000818:Animals; D005075:Biological Evolution; D004330:Drosophila / Q000145:classification* / Q000235:genetics; D008957:Models, Genetic; D009154:Mutation; D009343:Neisseria / Q000145:classification* / Q000235:genetics; D012641:Selection, Genetic; D013045:Species Specificity