Journal of Heredity Advance Access originally published online on October 3, 2008
Journal of Heredity 2009 100(1):97-105; doi:10.1093/jhered/esn078
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Original Articles |
Reduced X-Linked Rare Polymorphism in Males in Comparison to Females of Drosophila melanogaster
From the Department of Population Genetics, National Institute of Genetics, Yata 1111, Mishima, Shizuoka 411-8540, Japan (Takahashi and Takano-Shimizu); the Department of Genetics, Graduate University for Advanced Studies (SOKENDAI), Mishima, Shizuoka 411-8540, Japan (Tanaka and Takano-Shimizu); the Department of Applied Biology, Graduate School of Science and Technology, Kyoto Institute of Technology, Kyoto 606-8585, Japan (Itoh); the Insect Biomedical Research Center, Kyoto Institute of Technology, Kyoto, 606-8585, Japan (Itoh); the Department of Biosystems Science, Graduate University for Advanced Studies (SOKENDAI), Hayama, Kanagawa 240-0193, Japan (Takano-Shimizu); and the Department of Biological Science, Graduate School of Science, The University of Tokyo, Tokyo 113-8654, Japan (Takano-Shimizu)
Address correspondence to T. Takano-Shimizu at the address above, or e-mail: totakano{at}lab.nig.ac.jp.
Natural selection is assumed to act more strongly on X-linked loci than on autosomal loci because the fitness effect of a recessive mutation on the X chromosome is fully expressed in hemizygous males. Therefore, selection is expected to fix or remove recessive mutations on the X chromosome more efficiently than those on autosomes. However, the assumption that hemizygosity of the X chromosome selectively accelerates changes in allele frequency has not been confirmed directly. To examine this assumption, we investigated current natural selection on X-linked chemoreceptor genes in a natural population of Drosophila melanogaster by comparing nucleotide diversity, linkage disequilibrium (LD), and departure from the neutrality in 4 chemoreceptor genes on 100 X chromosomes each from female and male flies. The general pattern of nucleotide diversity and LD for the genes investigated was similar in females and males. In contrast, males harbored significantly fewer rare polymorphisms defined as singletons and doubletons. When all the gene sequences were concatenated, Tajima's D showed a significant departure from the neutrality in both females and males, whereas Fu and Li's F* value revealed departure only in males. These results suggest that some rare polymorphisms on the X chromosome from females are recessively deleterious and are removed by stronger purifying selection when transferred to hemizygous males.
Key Words: chemoreceptor gene • drosophila melanogaster • natural selection • rare polymorphism • X-linked polymorphism
Corresponding Editor: James Thompson
Received October 9, 2007
Revised July 21, 2008
Accepted August 18, 2008