title: First karyotype description of Hypostomus iheringii (Regan, 1908): a case of heterochromatic polymorphism.
abstract: In this study, which is the first karyotype analysis of Hypostomus iheringii, nine specimens collected in Córrego da Lapa (tributary of the Passa-Cinco River) showed a diploid number of 80 chromosomes. Silver nitrate staining and fluorescence in situ hybridization (FISH) with an 18S rDNA probe revealed the presence of multiple nucleolus organizer regions (NORs) (chromosome pairs 13, 20, and 34). FISH with a 5S rDNA probe showed that this cistron was only present in chromosome pair 2. When the karyotypes of individual animals were compared, unique heterochromatic polymorphisms were detected on chromosome pairs 1 and 5. Specifically, specimens had heterochromatic blocks (h+h+) on both chromosomes, one chromosome with heterochromatic blocks (h+h-) or chromosomes that lacked heterochromatic blocks (h-h-). Considering that heteromorphic pattern is not correlated with variation in size, the process of heterochromatinization might act on the long arms of these chromosomes. In summary, all chromosomal markers indicate that the karyotype of Hypostomus iheringii is highly differentiated and that the heterochromatinization of chromosomal segments may have contributed to its karyotypic differentiation.
authors.affiliation: Universidade Federal de São Carlos, Departamento de Genética e Evolução, Rodovia Washington Luís Km 235, São Carlos-SP, 13565-905, Brazil.
authors.forename: Josiane Baccarin
authors.initials: JB
authors.lastname: Traldi
authors.forename: Marcelo Ricardo
authors.initials: MR
authors.lastname: Vicari
authors.forename: Daniel Rodrigues
authors.initials: DR
authors.lastname: Blanco
authors.forename: Juliana de Fátima
authors.initials: Jde F
authors.lastname: Martinez
authors.forename: Roberto Ferreira
authors.initials: RF
authors.lastname: Artoni
authors.forename: Orlando
authors.initials: O
authors.lastname: Moreira-Filho
keywords: Hypostomini; chromosome variation; fish; heterochromatinization