Sister chromatid exchanges in the active and inactive X chromosomes

Sister chromatid exchange in chromosomes of cattle from three different breeds reared under similar conditions

A homogeneous group (same sex, age and environmental conditions) of 35 Italian cattle of the Podolian, Friesian, and Romagna breeds was investigated concerning the spontaneous incidence of sister chromatid exchange (SCE). The mean values of SCEs/cell were 7.9 +/- 3.4, 7.1 +/- 3.3, and 7.3 +/- 3.2 in the Podolian, the Friesian, and the Romagna breeds, respectively, with significant differences between the Podolian and the Friesian breeds. Simultaneous disclosure of SCEs and fluorescent G-bands in the lighter chromatid made possible the identification of chromosome 1, in addition to the biarmed X and Y chromosomes. The inter-chromosomal SCE-distribution revealed a nonrandom pattern due to significantly increased values of SCEs in chromosomes 1 and X, particularly in the Romagna breed.

Sister chromatid exchange in the goat (Capra hircus)

Lymphocyte cells from 30 Maltese and Syrian derivative goats (13 males and 17 females) reared in southern Italy underwent sister chromatid exchange (SCE) test. For the 902 cells we studied, the SCE-mean values were 6.6 +/- 3.0 per cell for both breeds. The SCE-frequency did not follow a Poisson distribution. The simultaneous visualization of SCEs and G-bands in the lightly stained chromatid allowed the study of SCE-distribution in chromosomes 1 and X. The number of SCEs in chromosome 1 was significantly higher (P > 0.001) than expected from relative chromosome length. No statistical differences between the numbers of SCEs in the active (early-replicating) and inactive (late-replicating) X-chromosomes of female cells were found.

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).

Sister-chromatid exchange rates in XX and XY cells of ten chimeric Callithrix jacchus individuals

In order to ascertain whether or not sister-chromatid exchange (SCE) differs in relation to sex, SCE rates in XX and XY cells from 10 specimens of marmoset (Callithrix jacchus) were examined. The choice of this primate is particularly suitable for three reasons: most individuals have a chimeric constitution, the X chromosome is quite large and the Y chromosome is particularly small. Therefore, the influence of possible differences in their exposure to the external environment can be eliminated. The results obtained did not reveal any significant difference between SCE rates in male and female cells in any of the examined individuals.

Effect of chloramphenicol on sister chromatid exchange in bovine fibroblasts

The genotoxic potential of different chloramphenicol concentrations (5, 20, 40 and 60 micrograms ml-1) was investigated in bovine fibroblast primary lines by sister chromatid exchange assay. Chloramphenicol acted for long enough to ensure similar effects to persistent storage in the kidney. In this experiment 10 micrograms ml-1 of 5-bromodeoxyuridine was added for 60 hours for all doses of chloramphenicol and to the control. When the tissue culture cells were exposed to increasing doses, increased numbers of sister chromatid exchanges developed. Differences were significantly different to the control.

Increased sister chromatid exchanges in human cell lines characterized by monosomy X or structural abnormalities of the X chromosome

In the present investigation we test the hypothesis that deficiencies of the X chromosome affect sister chromatid exchange (SCE) frequencies in human fibroblast cell lines. Our results show increased mean SCE frequencies in cell lines with abnormalities of the X chromosome: 45,X; 46,X,del(X) (q13), 46,X,del(X)(p11), and 46,X,i(Xq); control cell lines were 46,XX. In only one abnormal line [46,X,del(X)(p11)] was the increase not significant after correcting for multiple comparisons. If SCE formation is replication-dependent, the increased SCE frequencies might merely reflect the prolonged cell cycle we reported previously in cell lines with X chromosome abnormalities (Simpson and LeBeau 1981). Other explanations for differences between cell lines are possible, e.g., that deleted loci on the X chromosome affect cellular uptake of bromodeoxyuridine (BrDU). However, specific mechanisms were not explored directly.