Expression of transcription factor genes hoxb13a (A), six2a (B), tbx3a (C) and pax9 (D) in the caudal fin margin of the tail fin of adult males of Priapella lacandonae, Xiphophorus hellerii and X. maculatus, and X. hellerii females. (v, ventral, m, median, d, dorsal compartment). Vertical axis indicates fold change of expression normalized to cfm, m (A, C, D) or cfm, v(B). Data are represented as mean ± SEM. See also Figures S1, S2, S4.