Chromatid Aberrations Resulting from ³H-thymidine Incorporation into Early and Late S Periods in Human Fibroblasts

Summary

Chromatid aberrations have been induced by ³H-thymidine incorporated in early and late S periods of human XY, XXY and XX cells. At similar total ³H-disintegrations, late S cells are 4 times (XY) or 7 times (XXY) more sensitive than early S cells. This difference is partly due to (a) dose-rate differences between samples; early S samples receive irradiation at half the dose-rate of late S samples, and (b) localization differences of the ³H-thymidine in cells labelled at the two stages. In late S, label is concentrated over certain chromosomes, whereas in early S it is more evenly distributed. Localization produces an intranuclear dose-rate effect demonstrated by the concentration of aberrations to late-labelling chromosomes, particularly the late X. Any attempt at comparing stage sensitivity must be carried out at an intrachromosomal level.