Figure 4.
Branch segments on the discordant gene trees, (S 2, S 3) S 1 and (S 1, S 3) S 2, that can give rise to incompatible alleles isolating S 1 and S 2. In (A)–(D), a mutation on the left‐hand tree, (S 2, S 3) S 1, and a mutation on the right‐hand tree, (S 1, S 3) S 2, can give rise to a derived–derived incompatibility. These panels show all combinations of branch segments on which mutations could give rise to a derived–derived incompatibility on the pair of discordant trees shown. Panels (E) and (F) show all combinations of branch segments on which mutations could give rise to a derived‐ancestral incompatibility on this pair of trees. A mutation on branch segment j–k (red) leaves S 2 with an ancestral allele that can be incompatible with a derived allele produced by a mutation on branch segment a–d (blue) and inherited by S 1 (see main text).