Dose-response curves for simple and complex chromosome aberrations induced by X-rays and detected using fluorescence in situ hybridization.

A primary human fibroblast cell-line was grown to confluence and X-irradiated at 2, 4 and 6 Gy. The resulting chromosome aberrations were detected in first-division cells using a series of FISH assays in which either one or two chromosomes (nos. 1, 2, 4, 5, 7 and 13) and all centromeres were painted with distinct colours. Interchange aberrations were classed as simples if they appeared to originate from a break in each of two chromosomes (dicentric with fragment or reciprocal translocation), or complexes if their origins required three or more breaks in two or more chromosomes. Breaks not obviously connected with exchanges were also scored. The data were corrected to include paint patterns resulting from either incomplete or terminal exchanges. In addition we attempted to correct for the apparently simple exchanges which are actually derived from complex interactions (pseudosimples) using correction factors calculated by establishing the predominant complex families present at each dose. Power Law analysis of the corrected data showed a linear dose-response for simple exchanges and a dose-squared response for complex exchanges. Based upon this observation we suggest that simples result from lesions induced by the same radiation track and complexes arise from the interaction of lesions induced by separate tracks.