X-ray induced mutations, DNA and target theory

It is stated that X-ray induced, specific locus, germ-line mutation rates vary significantly in eukaryotes. A consideration of the radiobiology of the individual gene by the author leads to three major conclusions. (1) Mutation rates tend to be much lower than radiation theory predicts. (2) Selection and/or repair are major factors that determine the rates. (3) The mouse 7-locus test, which provides a principal data base for the standards of human radiation hygiene, may not provide adequate overall representation of the mutability of the mammalian genome, so more research is needed. (U.K.)