Comparison of types of chemically induced genetic changes in mammals

The present paper reviews the currently available in vivo systems for detection of chemically induced mutations and chromosome aberrations and summarizes the data of the relevant tests for mammalian germ-cell mutations (specific-locus test and heritable translocation test). The value of in vivo screening tests (somatic mutations and sperm abnormalities) for predicting specific-locus mutations is illustrated by comparing doubling doses. The results from the mammalian germ-cell mutation tests (specific-locus test and heritable translocation test) constitute the base-line for an assessment of predictability. Radiation and chemically induced specific-locus mutations differ in a number of respects, suggesting a need for caution in making risk estimates for chemical mutagen exposures in terms of radiation-equivalent doses. In vivo nondisjunction tests are discussed. Finally, unsolved problems and difficulties in generalizing qualitative and quantitative correlations between test systems are outlined. It is concluded that even qualitative predictions from data on somatic cells to germ cells are at best insecure because germ-cell specificity cannot be foretold, not to mention the fact that quantitative extrapolations from the results of in vivo screening tests, in general, are fraught with even more uncertainties. There is an acute need for collection of more data from studies involving germ cells.