SPONTANEOUS RATE OF SISTER-CHROMATID EXCHANGES (SCES) IN MITOTIC CHROMOSOMES OF SHEEP (OVIS-ARIES L) AND COMPARISON WITH CATTLE (BOS-TAURUSL), GOAT (CAPRA-HIRCUS L) AND RIVER BUFFALO (BUBALUS-BUBALIS L)

The spontaneous level of sister chromatid exchanges (SCEs) in the shee p, estimated by exposing peripheral blood lymphocytes in 0.1 mu g/ml o f 5'-bromodeoxyuridine (BrdU), was 4.08 +/- 2.47 SCE/cell, 2.04 SCE/ce ll cycle, 0.038 SCE/chromosome. The dose-response relationships, obser ved by exposing the cells to 0.1, 0.25, 0.5, 1.0, 2.5, and 5.0 mu g/ml of BrdU, rose rapidly from 0.1 to 0.25 mu g/ml, and less rapidly at h igher concentrations, thus reaching a saturation level. The analysis o f variance, performed on the square root transformed data at 0.1 and 5 mu g/ml of BrdU, indicated significant differences (P < 0.001) among the four donors tested. The distribution of the SCE/cell frequencies i n the cell population of the four donors followed the Poisson 'mixture ' probability function, thus confirming previous findings. The spontan eous rate of SCE/cell of sheep is compared with those previously repor ted for cattle, goat and river buffalo. The theoretical and practical implications of the spontaneous sister chromatid exchanges are discuss ed in relation to their possible use in animal production for (a) bett er genetic evaluation of the breeding animals under selection, (b) mor e precise monitoring of the genotoxic effects of environmental polluta nts.