Genomic signatures of selection at linked sites: unifying the disparity among species

Population genetics theory supplies powerful predictions about how natural selection, interacting with genetic linkage, will sculpt the genomic landscape of nucleotide polymorphism.Genetic hitch-hiking of neutral alleles linked to a beneficial mutation undergoing a 'hard' selective sweep, or the selective removal by background selection of deleterious mutations, will more greatly affect patterns of polymorphism in genomic regions with little recombination.Despite supporting evidence for genetic hitch-hiking and background selection from many organisms, empiricists have documented extreme disparities among species.The dominant features that could drive variation in linked selection among species include the potential roles for selective sweeps being 'hard' or 'soft' and the concealing effects of demography and confounding genomic variables.We advocate targeted studies of closely related species that differ in key variables to help clarify the causes of among-species disparities and to unify our understanding of how selection and linkage interact to shape genome evolution.