Dose-Yield Relationships for Individual Types of Chromosome Aberrations in Cells Irradiated in Early S

Abstract

The dose-yield relationships for individual classes of chromosome aberrations were measured for cells irradiated in early S after release from thymidine block. It was found that the yield for asymmetrical chromosome exchanges as a function of dose was quadratic, whereas that for sister unions was linear. These data cannot be reconciled with the Chadwick-Leenhouts hypothesis, which predicts that the initial lesion leading to aberration formation is always of a mixed one-hit, two-hit type, resulting in DNA double-stranded breaks. The data support the classical theory of aberration formation that initial lesions are of a one-hit type and that exchanges are of the two-hit type, involving two initial lesions, each of the one-hit type.