EFFECT OF TRITIATED THYMIDINE ON SISTER-CHROMATID EXCHANGE IN A RING CHROMOSOME

Peripheral lymphocytes from a human male heterozygous for a ring chromosome were cultured both in the presence and absence of tritiated thymidine. Analysis of colchicine-anaphase cells showed that incorporated triated thymidine induced a substantial increase in the frequency of dicentric ring chromosomes. Comparable levels of dicentrics in the first and second cell cycle following isotope incorporation indicated that dicentric induction is a dose (tritium)-independent process. The frequency of induced dicentrics, and hence of induced exchange between the sister ring chromatids, approximated the frequency of sister-chromatid exchange (determined autoradiographically) in rod chromosomes. This suggests, but does not prove, that sister-chromatid exchanges in rod chromosomes are radiation induced events. © 1969.