IDENTIFICATION OF NUCLEOLUS ORGANIZER CHROMOSOMES AND FREQUENCY OF ACTIVE NORS IN RIVER BUFFALO (BUBALUS-BUBALIS L)

Blood cells from 22 river buffaloes (Bubalus bubalis L., 2n = 50) rais ed in the South Italy were cultured for both early - and late - incorp oration of BrdU so as to obtain G- and R-banding, respectively. Slides were sequentially treated for G-banding/Ag-NOR and R-banding/Ag-NOR t echniques. These procedures allowed to identify which chromosomes carr y the NORs and the frequency of active NORs per NO-chromosome. Accordi ng to the standard nomenclature, NORs in river buffalo are located at the telomeres of chromosomes 3p, 4p, 6, 21, 23 and 24 while the freque ncies of active NORs per NO-chromosome were higher in chromosomes 4p, 23 and 24 (64.8%, 70.2% and 72.2%, respectively) than in chromosomes 3 p, 6 and 21 (42.1%, 17.3% and 28.1%, respectively).