Figure 1: The platyfish, X. maculatus.

(a) Female (top) and male (bottom) platyfish, of strain Jp163A with black pigment spots on the dorsal fin that develop when the activity of an X-chromosomal oncogene is appropriately controlled. In hybrid genotypes, this control is compromised, and malignant melanoma develops from the spots. (b) Phylogenetic position of the platyfish relative to other fish species.