Identification and description of distinct B chromosomes in Cyphocharax modestus (Characiformes, Curimatidae)

• Main Authors: Lessandra Viviane De Rosa Santos, Fausto Foresti, Cesar Martins, Claudio Oliveira, Adriane Pinto Wasko
• Format: Article
• Language: English
• Published: Sociedade Brasileira de Genética 2008-01-01
• Series: Genetics and Molecular Biology
• Subjects: B chromosomes; C-banding; Curimatidae; Cyphocharax modestus; supernumerary chromosomes
• Online Access: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1415-47572008000200019

Cytogenetic analyses were performed in Cyphocharax modestus, collected at Paranapanema River and Tietê River (São Paulo State, Brazil). A karyotype with 2n = 54 chromosomes was observed in the animals from both Brazilian freshwater river systems. One to four B chromosomes were also detected in individuals from the Paranapanema River, which represents the probable first report of more than a single supernumerary element in a species of the Curimatidae group. C-banding revealed centromeric and telomeric heterochromatin blocks in several chromosomes of the normal karyotype complement of C. modestus. Moreover, while some B chromosomes were characterized by the complete absence of C-bands, others were totally heterochromatic. Although there was a prevalence of B chromosomes in males of C. modestus, at least one supernumerary element was found in males and/or females of several other populations of the species, which suggests that the presence of these chromosomes seems to represent a general trait of C. modestus. A possible origin of the described B chromosomes may be related to the occurrence of a chromosome non-disjunction followed by the loss of euchromatic segments, an event that should have occurred in chromosomes that present conspicuous centromeric heterochromatic blocks and even in chromosomes that lack C-bands in this region, resulting in small supernumerary elements.