Functional constraints are similar in early and later stages of duplicate gene evolution in X. laevis paralogs. (A) Binned Ka/Ks of early (blue) and later (red) stages of duplicate gene evolution. (B) Regression of Ka/Ks versus Ks in the early and later stages indicates that selection (relaxed purifying + positive) is not more common in the early stage of duplicate gene evolution (blue dots) than the later stage (red dots). The Y-intercept of these regression lines was set to zero and Ka/Ks ratios greater 2 (including undefined ratios) were given a value of 2. In (A) and (B), a dashed line indicates the neutral expectation. Fragments with Ka/Ks > 2 are, on average, half of the size of those with Ka/Ks < 2. Ka/Ks ratios above 2 may therefore be attributable in part to stochastic variance in Ks .
Chain et al. BMC Evolutionary Biology 2008 8:43 doi:10.1186/1471-2148-8-43