The effects of sex-biased gene expression and X-linkage on rates of sequence evolution in Drosophila

Campos, J. L., Johnston, K. J.A. and Charlesworth, B. (2018) The effects of sex-biased gene expression and X-linkage on rates of sequence evolution in Drosophila. Molecular Biology and Evolution, 35(3), pp. 655-665. (doi: 10.1093/molbev/msx317) (PMID:29228267)

Abstract

A faster rate of adaptive evolution of X-linked genes compared with autosomal genes (the faster-X effect) can be caused by the fixation of recessive or partially recessive advantageous mutations. This effect should be largest for advantageous mutations that affect only male fitness, and least for mutations that affect only female fitness. We tested these predictions in Drosophila melanogaster by using coding and functionally significant noncoding sequences of genes with different levels of sex-biased expression. Consistent with theory, nonsynonymous substitutions in most male-biased and unbiased genes show faster adaptive evolution on the X. However, genes with very low recombination rates do not show such an effect, possibly as a consequence of Hill–Robertson interference. Contrary to expectation, there was a substantial faster-X effect for female-biased genes. After correcting for recombination rate differences, however, female-biased genes did not show a faster X-effect. Similar analyses of noncoding UTRs and long introns showed a faster-X effect for all groups of genes, other than introns of female-biased genes. Given the strong evidence that deleterious mutations are mostly recessive or partially recessive, we would expect a slower rate of evolution of X-linked genes for slightly deleterious mutations that become fixed by genetic drift. Surprisingly, we found little evidence for this after correcting for recombination rate, implying that weakly deleterious mutations are mostly close to being semidominant. This is consistent with evidence from polymorphism data, which we use to test how models of selection that assume semidominance with no sex-specific fitness effects may bias estimates of purifying selection.

• Item Type: Articles
• Additional Information: This work was supported by Grant RPG-2015-2033 from the Leverhulme Trust (to B.C.).
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Johnston, Ms Keira
• Authors: Campos, J. L., Johnston, K. J.A., and Charlesworth, B.
• College/School: College of Medical Veterinary and Life Sciences > School of Health & Wellbeing > Public Health
• Journal Name: Molecular Biology and Evolution
• Publisher: Oxford University Press
• ISSN: 0737-4038
• ISSN (Online): 1537-1719
• Published Online: 08 December 2017
• Copyright Holders: Copyright © 2017 The Author
• First Published: First published in Molecular Biology and Evolution 35(3):655-665
• Publisher Policy: Reproduced in accordance with the copyright policy of the publisher