The frequency of gross chromosomal aberrations (CA) and of sister chromatid exchanges (SCE) was measured in cells X-irradiated while in the density-inhibited plateau phase of growth. When the cells were subcultured immediately after irradiation with 0 to 800 rad, CA increased exponentially with dose, whereas SCE increased about twofold with doses up to 100 rad but declined with higher doses (200-400 rad). When subculture was delayed to facilitate repair, CA declined and reached a minimum level after 4-6 hr of repair time. Delayed subculture during this interval led to an enhancement in SCE; with longer repair times, SCE declined and reached spontaneous levels by 12-24 hr. CA appear to be related to cell killing, whereas SCE correlate more closely with changes in the frequency of malignant transformation induced under similar conditions by X irradiation.

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Copyright 1981 Academic Press, Inc.
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