In Drosophila, plants and mammals, genes located in regions of the genome where the frequency of genetic recombination is unusually low have reduced levels of intra-specific DNA sequence variation. In addition, measures such as codon usage bias suggest reduced levels of adaptation in regions of low recombination in Drosophila and in non-recombining organelle genomes. One factor that may contibute to these patterns is the effect of selection on variability and evolution at linked sites. Models of a number of evolutionary processes that can produce such effects (genetic hitchhiking, background seletion, Muller's ratchet, and Hill-Robertson interference betwen weakly selected sites) will be described. Possible methods for testing for the action of these processes will also be discussed.
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