1 September 2009 Effective Population Size and the Faster-X Effect: An Extended Model
Beatriz Vicoso, Brian Charlesworth
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Current models of X-linked and autosomal evolutionary rates often assume that the effective population size of the X chromosome (NeX) is equal to three-quarters of the autosomal population size (NeA). However, polymorphism studies of Drosophila melanogaster and D. simulans suggest that there are often significant deviations from this value. We have computed fixation rates of beneficial and deleterious mutations at X-linked and autosomal sites when this occurs. We find that NeX/NeA is a crucial parameter for the rates of evolution of X-linked sites compared to autosomal sites. Faster-X evolution due to the fixation of beneficial mutations can occur under a much wider range of levels of dominance when NeX/NeA > ¾. We also examined various parameters that are known to influence the rates of evolution at X-linked and autosomal sites, such as different mutation rates in males and females and mutations that are sexually antagonistic, to determine which cases can lead to faster-X evolution. We show that, when the rate of nonsynonymous evolution is normalized by the rate of neutral evolution, a sex difference in mutation rate has no influence on the conditions for faster-X evolution.

© 2009 The Society for the Study of Evolution.
Beatriz Vicoso and Brian Charlesworth "Effective Population Size and the Faster-X Effect: An Extended Model," Evolution 63(9), 2413-2426, (1 September 2009). https://doi.org/10.1111/j.1558-5646.2009.00719.x
Received: 19 January 2009; Accepted: 1 March 2009; Published: 1 September 2009

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effective population size
faster-X effect
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