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Abstract
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 (Ba) 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 (BM) and microchromosome (Bm). 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.
Acknowledgments
The authors wish to thank Fernando C.P. D’Agosta and Ricardo M.C. Castro for the taxonomical identification. This work was supported by grants from Fundação de Amparo à Pesquisa do Estado de São Paulo – FAPESP (Proc. 2010/06919-8, 2011/15007-5) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq).