Hashimoto, Diogo Teruo [UNESP]Voltolin, Tatiana Aparecida [UNESP]Valim de Arruda Paes, Ana Danyelle Noitel [UNESP]Foresti, Fausto [UNESP]Bortolozzi, Jehud [UNESP]Porto-Foresti, Fábio [UNESP]2014-05-202014-05-202012-01-01Comparative Cytogenetics. St Petersburg: Zoological Inst, v. 6, n. 2, p. 141-151, 2012.1993-0771http://hdl.handle.net/11449/18767The aim of this study was to characterize cytogenetically one population of the fish Moenkhausia sanctaefilomenae (Steindachner, 1907), with emphasis on the analysis of B chromosomes. The nucleolar activity in the B microchromosomes was characterized, and an analysis of mitotic instability of these microchromosomes was accomplished. The results showed a diploid chromosome number of 50 chromosomes. In all individuals, we observed the presence of B microchromosomes with intra- and inter-individual variability. The analysis of the nucleolus organizing regions (NORs) by silver nitrate staining demonstrated multiple NORs. We observed active sites of ribosomal DNA in the B microchromosomes, with a frequency of 20% in the analyzed cells, which shows gene activity in these chromosomal elements. The analysis of constitutive heterochromatin patterns showed that the B microchromosomes are heterochromatic or euchromatic, which demonstrates differentiation of DNA composition between these genomic elements. The calculation of the mitotic instability index implied that B chromosomes in this species might be in a final stage of instability.141-151engfish cytogeneticNOR expressionsupernumerary chromosomesmitotic instabilityArtigo10.3897/CompCytogen.v6i2.1769WOS:000307194600004Acesso abertoWOS000307194600004.pdf3815338174165832