Kinetics of the Formation of Chromosome Aberrations in X-Irradiated Human Lymphocytes: Analysis by Premature Chromosome Condensation with Delayed Fusion

Human lymphocytes irradiated with graded doses of up to 5 Gy of 150 kV X rays were fused with mitotic CHO cells after delay times ranging from 0 to 14 h after irradiation. The yields of dicentrics seen under PCC conditions, using C-banding for centromere detection, and of excess acentric fragments observed in the PCC experiment were determined by image analysis. At 4 Gy the time course of the yield of dicentrics shows an early plateau for delay times up to 2 h, then an S-shaped rise and a final plateau which is reached after a delay time of about 8 to 10 h. Whereas the dose-yield curve measured at zero delay time is strictly linear, the shape of the curve obtained for 8 h delay time is linear-quadratic. The linear yield component, αD, is formed entirely in the fast process manifested in the early plateau, while component $\beta D^{2}$ is developed slowly in the subsequent hours. Analysis of the kinetics of the rise of the S-shaped curve for yield as a function of time leads to the pos...