Sister chromatid exchange (SCE) in cattle: a comparison between normal and rob (1;29)-carrying karyotypes.

Fifty-one phenotypically normal Maronesa cattle (28 males and 23 females) from North-Portugal were studied to ascertain the frequency of SCEs in normal karyotypes and in karyotypes carrying rob (1;29). In the 1852 examined cells, the mean value of SCEs was 7.1 +/- 3.6. In the 841 cells from 23 normal karyotype animals the mean value of SCEs was 6.6 +/- 3.6; in the 611 cells from 17 heterozygous carriers of rob (1;29) the mean value of SCEs was 7.1 +/- 3.3; in 400 cells from 11 homozygous carriers the mean value of SCEs was 8.1 +/- 3.8. All these differences were highly significant (P < 0.001). No statistical differences were found between the mean values of SCEs in male (7.0 +/- 3.7) and female (7.1 +/- 3.5) cells in the total sampling. However, in 280 cells from two pairs of heterosexual twins, we found that the mean value of SCEs in female cells (7.9 +/- 3.0) was significantly higher than that in male cells (5.7 +/- 3.1).