Monday, June 8, 2009
Drosophila genome under selection
Over the past four decades, the predominant view of molecular evolution saw little connection between natural selection and genome evolution, assumed that the functionally constrained fraction of the genome was relatively small, and that adaptation was sufficiently infrequent and played little role in shaping patterns of variation within and between species. In a paper that just came out in PLoS Genetics, Guy Sella, Dmitri Petrov, Molly Przeworski and Peter Andolfatto review recent evidence from Drosophila which strongly implies that this view is invalid. Analyses of genetic variation within and between species reveal that much of the Drosophila genome is under purifying selection, and thus of functional importance, and that a large fraction of coding and non-coding differences between species are adaptive. The findings further indicate that, in Drosophila, adaptations may be both common and strong enough that the fate of neutral mutations depends on their chance linkage to adaptive mutations as much as on the vagaries of genetic drift. The emerging evidence has implications for a wide variety of fields, from conservation genetics to bioinformatics, and presents challenges to modelers and experimentalists alike. The papers from our lab that are reviewed here include a paper on pesticide resistance in Drosophila (Aminetzach et al, 2005) and two papers providing evidence that adaptation is common and involves strong selection in Drosophila (Macpherson et al., 2007) and that it is common and significantly affects evolution of neutral sites in humans (Cai et al., 2009).