B chromosome dynamics in (Teleostei, Characiformes) and comparisons with supernumerary chromosome system in other species.

Within the genus Agassiz, 1829, five species are known to carry B chromosomes, i.e. chromosomes beyond the usual diploid number that have been traditionally considered as accessory for the genome. Chromosome microdissection and mapping of repetitive DNA sequences are effective tools to assess the DNA content and allow a better understanding about the origin and composition of these elements in an array of species. In this study, a novel characterization of B chromosomes in Valenciennes, 1850 (2n=54) was reported for the first time and their sequence complementarity with the supernumerary chromosomes observed in (Valenciennes, 1836) and Agassiz, 1829 was investigated. The hybridization patterns obtained with chromosome painting using the micro B probe of and the satDNA SATH1 mapping made it possible to assume homology of sequences between the B chromosomes of these congeneric species. Our results suggest that the origin of B chromosomes in the genus is a phylogenetically old event.