Cytogenetic characterization of distinct B chromosomes in a population of the fish Astyanax bockmanni (Teleostei, Characiformes)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Processo FAPESP: 10/06919-8

Processo FAPESP: 11/15007-5

Individuals of Astyanax bockmanni from one population belonging to the Paranapanema River basin, southeastern Brazil, were cytogenetically examined. In the present paper, we report a diploid number of 50 chromosomes, with some individuals bearing additional chromosomes, characterized as different variants of B chromosomes. The B microchromosome of acrocentric morphology (B-a) was the most frequent type in this population (77.7%). Two other variants were identified as metacentric B chromosomes, but of distinct sizes, characterized as macrochromosome (B-M) and microchromosome (B-m). Conspicuous heterochromatic blocks were observed in the terminal regions of some chromosomes of the standard karyotype and partially heterochromatic blocks were detected in all B chromosomes. 18S ribosomal RNA genes were distributed in the terminal region of several chromosomes, but were not located on the B chromosomes.