Regiões organizadoras de nucléolos em búfalos das raças murrah, jafarabadi e mediterrânea, do estado de São Paulo

The nucleolus organizer regions (NORs) were studied in 50 river buffaloes (2n = 50), from the State of Sao Paulo, being 19 Murrah, 17 Jafarabadi and 14 Mediterranean. In the three breeds, NORs were located in six chromosome pairs, on the telomeric regions identified as 3p, 4p, 8q, 21q, 23q, and 24q. The mean numbers of NORs per cell were not significantly different (p > 0.01) among each breed of buffaloes. Several types of NORs associations occurred and the most frequently observed involved two NORs located in acrocentric chromosomes. The correlation coefficient between the number of NORs and the number of associations was statistically significant (p < 0.01) for each breed. The animais of the three breeds showed predominantly the +/- NOR pattern for the pairs 3, 4 and 8, that is, only one of the homologues of each pair exhibited genetically active NOR. The frequency of NORs was highest for pair 3 and lowest for pair 8, in the Mediterranean and Jafarabadi breeds, while in Murrah, it was highest for one of the small acrocentric and lowest for pair 4.