Genetics, Vol. 179, 1135-1141, June 2008, Copyright © 2008
doi:10.1534/genetics.107.083428

The Anomalous Effects of Biased Mutation Revisited: Mean–Optimum Deviation and Apparent Directional Selection Under Stabilizing Selection

Institute of Evolutionary Biology, University of Edinburgh, Edinburgh EH9 3JT, United Kingdom

1 Corresponding author: Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, W. Mains Rd., Edinburgh EH9 3JT, United Kingdom.
E-mail: xu-sheng.zhang{at}ed.ac.uk

Empirical evidence indicates that the distribution of the effects of mutations on quantitative traits is not symmetric about zero. Under stabilizing selection in infinite populations with normally distributed mutant effects having a nonzero mean, Waxman and Peck showed that the deviation of the population mean from the optimum is expected to be small. We show by simulation that genetic drift, leptokurtosis of mutational effects, and pleiotropy can increase the mean–optimum deviation greatly, however, and that the apparent directional selection thereby caused can be substantial.