Changes in frequencies of chromosomal aberrations and sister chromatid exchanges during confluent holding recovery in X-irradiated normal human diploid fibroblasts.

The time course of the changes in survival and cytogenetic damage was studied in X-irradiated cultures of human diploid fibroblasts before release from density-inhibition of growth. The frequency of chromosomal aberrations declined rapidly during the initial 2 h recovery interval in parallel with an enhancement in survival. The frequency of sister chromatid exchanges (SCE) increased during this interval reaching a maximum of 2 h, then declined. These changes are discussed in relation to previous observations on X-ray induced cytogenetic damage and malignant transformation in rodent cells under similar conditions.