Cytogenetics of Bisexual/Unisexual Species of Poecilia: II. Analysis of Heterochromatin and Nucleolar Organizer Regions in Poecilia Mexicana Mexicana by C-Banding and DAPI, Quinaerine, Chromomycin a\u3csub\u3e3\u3c/sub\u3e, and Silver Staining

Chromosomes of Poecilia mexicana mexicana, one of the bisexual species involved in the hybrid origin of the unisexual teleost fish species P. formosa, were analysed by several staining techniques. Sex-specific, differential heterochromatin, found in other congeneric species, was not observed in P. m. mexicana. Nucleolar organizer regions were polymorphic among individual specimens within a given population sample. A single specimen exhibiting intraindividual variability of chromosome pair 1 and a specimen with a triploid karyotype are also described