Pattern Development in the Platyfish,. 1X:phophorus maculatus

Pigment (macromelanophore) patterns in the platyfish Xiphophorus maculatus are due to a complex pigmentary locus; for example, the spotted-dorsal (Sd) fin pattern is due to the Sd locus. In interspecific backcross hybrids with the swordtail X. helleri, the Sd pattern changes into benign or malignant dorsal fin melanoma as a result of hemi- or homozygous loss of a platyfsh regulatory (R) gene, the tumor suppressor gene Duff, that appears to play a role in the final differentiation of macromelanophores. Closely linked to the pigmentary locus is an epidermal growth fador receptor-like gene, Xmrk-2, that has arisen by duplication from the linked Xmrk-1. The transcriptional expression of the Xmrk genes was determined in various tissues including Sd pigment patterns and melanomas o