X-ray induced mutations, DNA and target theory

Abstract

THAT X-ray induced, specific locus, germ-line mutation rates vary significantly in eukaryotes is generally known, but the factors that are responsible for such differences have not been assessed in detail. It was recently proposed¹ for a variety of species that mutability is closely and simply related to total DNA per genome. This approach, however, has not stood the test of critical review²; in fact, even within one species (mouse) there are major differences between the rates for different genes, and even for different germ cells^3–5. I have therefore taken a different approach by considering the radiobiology of the individual gene. The analysis 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.