Gene conversion and natural selection in the evolution of gene duplications in Drosophila melanogaster

We have investigated the role played by sex chromosome in Drosophila on the evolution of gene families. Sex chromosomes are of particular interest because hemizygosity of the X in males has long-term implications for the roles of recessive advantageous mutations and deleterious mutations in evolution. We have found that the rates of sequence divergence are higher by approximately a factor of two amongst X-linked duplicates compared with autosomal duplicates. This X-autosome contrast suggests that recessive advantageous mutations are playing a significant role in gene family evolution in Drosophila. Polymorphism data from X-linked gene families reveals an excess of divergence between copies relative to polymorphism, and there is evidence for selective constraint at all loci, providing further evidence for natural selection in the divergence of X-linked families. By contrast, autosomal families show a paucity of divergence that is attributable to long-term concerted evolution by gene conversion between paralogs.