Fig. 3.

The number of expected A > G mutations of ancestrally strongly edited sites based on the HPM. According to HPM, all ancestral strong editing sites are either A-preferring or G-preferring. A-preferring sites are neutral or slightly deleterious, and thus an upper bound to their incidence rate at the ancestral node (lower black circle) is obtained from the incidence rate of synonymous sites at the same node. The remaining sites are G-preferring (a lower bound). Mutations are expected to accumulate along the evolutionary path from the above ancestral node to each of the descendants (thick black line). A-preferring sites are expected to mutate along this path at a rate higher than the background nonsynonymous mutation rate, and G-preferring sites are expected to mutate at a rate higher than the neutral (synonymous) rate. Together, one obtains a conservative estimate to the number of mutations expected based on HPM, to be compared with the observed numbers.