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Hitchhiking effects of recurrent beneficial amino acid substitutions in the Drosophila

Summary: Hitchhiking effects of recurrent beneficial amino
acid substitutions in the Drosophila
melanogaster genome
Peter Andolfatto1
Division of Biological Sciences, University of California San Diego, La Jolla, California 92093, USA
Several recent studies have estimated that a large fraction of amino acid divergence between species of Drosophila was
fixed by positive selection, using statistical approaches based on the McDonald-Kreitman test. However, little is
known about associated selection coefficients of beneficial amino acid mutations. Recurrent selective sweeps
associated with adaptive substitutions should leave a characteristic signature in genome variability data that contains
information about the frequency and strength of selection. Here, I document a significant negative correlation
between the level and the frequency of synonymous site polymorphism and the rate of protein evolution in highly
recombining regions of the X chromosome of D. melanogaster. This pattern is predicted by recurrent adaptive protein
evolution and suggests that adaptation is an important determinant of patterns of neutral variation genome-wide.
Using a maximum likelihood approach, I estimate the product of the rate and strength of selection under a recurrent
genetic hitchhiking model, 2Nes 3 10-8
. Using an approach based on the McDonald-Kreitman test, I estimate that
50% of divergent amino acids were driven to fixation by positive selection, implying that beneficial amino acid
substitutions are of weak effect on average, on the order of 10-5
(i.e., 2Nes 40). Two implications of these results
are that most adaptive substitutions will be difficult to detect in genome scans of selection and that population size


Source: Andolfatto, Peter - Department of Ecology and Evolutionary Biology, Princeton University


Collections: Biology and Medicine