Fig. 5.

Gene trees predicted under two hypotheses for the direction of introgression. X and Y chromosomes are shown in blue and red, respectively; the origin of a new Y is shown as a diamond. The abbreviations for the species names are given in figure 1. (A) Introgression of Chr 12 from Pungitius sinensis into P. pungitius creates the P. pungitius Y chromosome (left). This generates a gene tree in which those two lineages are sister to P. tymensis (right). (B) Introgression of the Y from P. pungitius into P. sinensis generates a gene tree in which those two lineages are sister to the P. pungitius X chromosomes. (C) The gene tree from the SDR of Chr 12 (10–12 Mb) supports hypothesis (A). The numbers indicate the number of sampled chromosomes in each clade.