Cytogenetics of Bisexual/Unisexual Species of Poecilia I. C-Bands, Ag-nor Polymorphisms, and Sex Chromosomes in Three Populations of Poecilia Latipinna

Three populations of the North American cyprin-odont fish Poecilia latipinna, considered to be one of the progenitor species of the gynogenetic unisexual P.formosa. were analyzed by C-banding and Ag-staining. C-bands were found to be polymorphic, and Ag-staining showed a high degree of variability in both the number and location of nucleolus organizer regions. The C-banding and Ag-staining patterns allow, to a certain extern. to distinguish individual specimens from each of these populations. Females of the three populations were found to have a het-eromorphic chromosome pair, which was frequently identifiable with Giemsa staining and always after C-banding. This pair could be interpreted as sex chromosomes of the ZWZZ type