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 Neissseria, 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.
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References
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Smith, J.M. Estimating selection by comparing synonymous and substitutional changes. J Mol Evol 39, 123–128 (1994). https://doi.org/10.1007/BF00163800
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DOI: https://doi.org/10.1007/BF00163800