Induction of sister chromatid exchanges in chromosomes of rat kangaroo cells by tritium incorporated into DNA

Abstract

The frequency of sister chromatid exchanges increases with increasing amounts of incorporation of 3H-thymidine into the chromosomes of a line of rat kangaroo cells. The relation only holds over a range of very low levels of incorporated radioactivity. Increases in the incorporated radioactivity above the amount necessary to produce about 0.4 grains/day along the length of the chromosome in autoradiographs does not result in any further increase in the frequency of exchanges. Sister chromatid exchanges therefore appear to be induced by the tritium that must be incorporated in order to detect the exchanges. The data suggest that all exchanges are radiation-induced, and that no exchanges occur spontaneously.