RESUMO
An investigation to understand the dynamics and biological significance of fragile site expression, and identification of 5-fluorodeoxyuridine (FUdR) induced chromosomal gaps/breaks, were carried out in an experimental flock of 45 Suffolk sheep. The statistical comparison revealed, highly significant variation in the frequency of chromosomal fragile site expression between control and FUdR cultures. Mean (+/- S.D.) values for cells with gaps and breaks, or aberrant cell count (AC), and the number of aberrations (NoA) per animal were 2.02 +/- 0.34, 2.42 +/- 0.48, 13.26 +/- 0.85 and 21.87 +/- 1.88 (P lessthan 0.01) in control and FUdR cultures, respectively. The comparison of age revealed nonsignificant variation between control and FUdR cultures. The G-band analysis of fragile site data revealed gaps in 29 autosomal and two X-chromosomal bands in the control cultures, whereas FUdR treated cultures scored 78 unstable bands in autosomes of which 56 were significantly fragile. X-chromosomes expressed breaks and gaps in six G-negative bands and five of them (Xq13, Xq15, Xq17, Xq24 and Xq26) were significantly fragile. The distribution comparison of autosomal fragile sites between sex groups did not reveal any significant variation. Female X-chromosomes were significantly more fragile than the male X-chromosomes. The distribution comparison for age groups (lambs versus adults) revealed significantly higher number of fragile bands in adults. Comparison of published data on reciprocal translocations in sheep with the fragile-site data obtained in this study indicated that the break sites of both phenomena were correlated. Similarities were also found between fragile sites and breakpoints of evolutionary significance in family Bovidae.