title: A highly differentiated ZZ/ZW sex chromosome system in a Characidae fish, Triportheus guentheri.
abstract: Seventeen specimens of Triportheus guentheri, a fish of the family Characidae, were submitted to chromosomal analysis, with a highly differentiated heteromorphic ZW pair being detected. Chromosome W is much smaller than chromosome Z and mostly heterochromatic. Chromosome Z is the largest in the karyotype, with heterochromatin occurring in the telomeric and centromeric regions only. The W chromosome also varies somewhat in size, the variations being probably due to its long arm. In addition to two other autosomal pairs, chromosome Z shows also an occasional Ag-NOR. Aspects of the ZW system differentiation and of the NOR presence in chromosome Z are discussed. The Characidae family includes a great deal of neotropical freshwater fish species and Triportheus appears to represent the only genus in this family having sex chromosome differentiation at a cytological level.
authors.affiliation: Departamento de Genética e Evolução, Universidade Federal de São Carlos, Brazil.
authors.forename: L A
authors.initials: LA
authors.lastname: Bertollo
authors.forename: Z I
authors.initials: ZI
authors.lastname: Cavallaro
mesh_terms: D000818:Animals; D001938:Brazil; D005260:Female; D005399:Fishes / Q000235:genetics*; D007621:Karyotyping; D008297:Male; D009697:Nucleolus Organizer Region; D012730:Sex Chromosomes