A linear dose response was observed for radon-induced mutations at the CHO-hprt locus with an induction frequency of$1.4\times 10^{-4}$ mutants per viable cell per gray. Mutants isolated after two levels of radon exposure were evaluated using Southern blot techniques and polymerase chain reaction (PCR) exon amplification. No significant differences in mutational spectra were detected at these two exposure levels. Of 52 radon-induced mutations, 48% sustained a gene deletion, 23% underwent a rearrangement of the banding patterns or loss of one or more exons, and 29% showed no change from the parental line. These mutants were compared with mutants produced after X irradiation (3 Gy) and with spontaneous mutants from untreated cells. The spectra of mutation types in cells treated with radon and X rays were not significantly different. In contrast, 31 spontaneous mutations exhibited a low percentage of gene deletion events (16%); most spontaneous mutants showed no change (74%); the remaining 10% were classified as alterations. In conclusion, the principal lesion seen at the CHO-hprt locus after radiation exposure in gene deletion, while the predominant class of spontaneous mutations is composed of smaller events not detectable by Southern blot or PCR exon analysis.

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