Study of chromosome lesions induced by gamma-rays during the G2 and mitotic phases of the cell cycle.

Irradiation with 2 Gy of gamma-rays was performed on synchronized human lymphocytes 5 to 120 min before harvesting in order to study chromosome sensitivity during the G2-phase and during the different stages of mitosis. It was found that chromosome lesions, consisting mostly of chromatid breaks, could be induced at any stage and that radiation must occur at least 10 min before chromosome harvest for the chromosome damage to be exhibited. Chromatid exchanges were rarely observed and required a much long lapse time between radiation treatment and harvest. The most radiation sensitive period was found to be the end of G2.