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Abstract
Three specimes of Baryancistrus aff. niveatus were studied cytogenetically by conventional staining, C banding, Ag-NORs, CMA3, DAPI and FISH with human telomeric probes. The results revealed a complement consisting of 52 metacentric, submetacentric and subtelocentric type chromosomes. C banding showed that heterochro-matin is located at pairs 1, 3, 6, 10, 11 and 22 in different positions. NORs were located at the short arm of pair 3, coinciding with a positive C-band. This region was also marked with CMA3, which also marked heterochromatic blocks in chromosomes 11 and 22. These regions were negatively stained by DAPI. These results revealed the presence of two different types of constitutive heterochromatin, probably due to their base composition. Chromosome bearing rDNA sites presented a difference in size in the NOR regions, probably due to heterochromatin and ribos-somal cistrons amplification. The localization of telomeric sequences by FISH revealed the conservative nature of this region.
