Sister chromatid exchange points (SCE points) on individual chromosomes were studied in cultured lymphocytes from 11 monozygotic (MZ) and nine dizygotic (DZ) same-sexed pairs by means of sequential Q-banding and BUdR-Giemsa techniques. No statistically significant variation between unrelated individuals with respect to SCE points on specific chromosomes was found. Intrapair differences in the number of SCE points on specific chromosomes were not significantly smaller between MZ twin partners as compared with DZ partners. The results suggest that genetic factors do not play any major role in the frequency and distribution of SCE in normal subjects.
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