title: Evolutionary aspects of the ZZ/ZW sex chromosome system in the Characidae fish, genus Triportheus. A monophyletic state and NOR location on the W chromosome.
abstract: Four species/populations of Triportheus, T. guentheri, T. cf. elongatus and T. paranense from different Brazilian hydrographic basins, were studied cytogenetically. All the species showed a similar karyotypic macrostructure, with a diploid chromosome number 2n = 52 and a ZZ/ZW sex chromosome system. Besides silver- and fluorochrome-staining, the chromosome mapping of 18S rDNA was also investigated using a biotinylated probe. In spite of some variation in the number of the NORs, a major chromosome site was always present on the short arm of an autosomal pair. In addition, a characteristic rDNA site was also observed on the telomeric region of the W chromosome in the four species/populations. In Triportheus differential reduction in size and heterochromatin accumulation appear to be the main processes associated with the evolution of the sex W chromosome. The location of rRNA genes on this chromosome may correspond to a plesiomorphic condition in the genus and, if so, predates to the sex chromosome system differentiation, with a possible influence in the initial steps of this process.
authors.affiliation: Universidade Estadual de Ponta Grossa, Campus de Uvaranas, Departamento de Biologia Geral, 84030-900 Ponta Grossa, PR, Brazil. rfartoni@uol.com.br
authors.forename: R F
authors.initials: RF
authors.lastname: Artoni
authors.forename: L A C
authors.initials: LA
authors.lastname: Bertollo
mesh_terms: D000818:Animals; D005075:Biological Evolution; D002871:Chromosome Banding; D004275:DNA, Ribosomal; D005260:Female; D005399:Fishes / Q000235:genetics*; D017404:In Situ Hybridization, Fluorescence; D007621:Karyotyping; D008297:Male; D009697:Nucleolus Organizer Region / Q000235:genetics*; D012730:Sex Chromosomes; D019849:Sex Determination Processes
chemical_list: D004275:DNA, Ribosomal