W→S substitutions (red) increase with acceleration, while S→W substitutions (blue) do not.
(A) Proportion of all bases that have W→S and S→W changes versus acceleration in our genome-wide scan of 34,498 elements. The mean proportion of each type of substitution is plotted for four groups based on the amount of acceleration as quantified by the LRT: extreme (p < 4.5e−4), high (4.5e−4 ≤ p < 0.05), medium (0.05 ≤ p < 0.1), and low (p ≤ 0.1). These groups correspond to HAR1–HAR5, HAR6–HAR49, HAR50–HAR202, and the remaining ~34,000 conserved elements. The normal 95% confidence interval for each mean is shown with dotted lines. These are estimates of the unconditional probability P(human = S, ancestor = W) that a base is strong in human and weak in the ancestral consensus sequence, and vice versa. The differences between substitution types are statistically significant in the extreme and high groups.
(B) The same plot, but dividing by the proportion of ancestral bases that are weak or strong. These are estimates of the conditional probability P(human = S| ancestor = W) that a base is strong in human, given that the ancestral base is weak, and vice versa. The differences between substitution types are significant in the extreme group only.