SUSCEPTIBILITY TO THE DEVELOPMENT OF PIGMENT CELL TUMORS IN A CLONE OF THE AMAZON MOLLY, POECILIA-FORMOSA, INTRODUCED THROUGH A MICROCHROMOSOME

The Amazon molly Poecilia formosa is a gynogenetic fish that reproduce s through the development of ameiotic diploid eggs triggered by insemi nation by males of related species without following karyogamie, This leads to clonal offspring, In rare cases, however, this gynogenesis is leaky, and paternal DNA in the form of small supernumerary chromosome s is included into the maternal genome, We have obtained a clone where one such microchromosome contains a pigmentary locus, resulting in ma cromelanophore pigmentation of the carrier, Approximately 5% of these fish spontaneously develop exophytic nodular or papillomatous pigment cell tumors, The tumors display considerable differences with respect to growth characteristics and invasiveness, despite the genetic unifor mity of the affected animals, Following transplantation to syngeneic b ests, a remarkable clonal variability was observed, Oncogenes that are involved in tumorigenesis in hereditary melanoma of the closely relat ed bh Xiphophorus appear not to be instrumental for induction of the P . formosa pigment cell tumors, Moreover, a new genetic locus is define d that mediates susceptibility to pigment cell tumor development and l eads to transformation of chromatoblasts.