The proliferation of sequenced genomes has permitted the
evaluation of the role of natural selection at that level of organization.
Studies have shown that some species, such as Drosophila melanogaster, showpositive Darwinian selection in relatively large number of genes, whereas other
species, such as Arabidopsis thaliana show very low levels of positive
selection compared to purifying or negative selection. By comparison Homo
sapiens show intermediate levels of positive selection.
Such studies have in
common an evaluation of selection within a single lineage but generally do not
address selection that may be occurring as new species arise, that is at splits
in their respective phylogenetic trees. A few studies have targeted selection
as species diverge but most of them are restricted to evaluating SNPs scattered
throughout the genome and not whole sequences of genes. Using this approach,
one may infer whether selection is common or rare during speciation but not
necessarily whether selection is associated with particular functional groups
of genes, which in turn may inform hypotheses on the genetics of speciation.(Read more)
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