Relationship between unscheduled DNA synthesis and mutation induction in male mice.

Unscheduled DNA synthesis (UDS) induced in the germ cells of male mice by chemical and physical agents can be studied in vivo by making use of the timing of spermatogenesis and spermiogenesis. In meiotic and postmeiotic germ-cell stages, UDS occurs from leptotene through midspermatid stages but is not detected in later stages. No consistent correlation has been seen between the occurrence of UDS in the germ cells and reduced dominant lethal frequencies or reduced specific-locus mutation frequencies. It is suggested that the UDS observed in the germ cells may be principally involved in the removal of DNA lesions which, if left, could give rise to subtle genetic damage that current mammalian genetic tests may not be able to detect. Characterization of mouse stocks with reduced UDS capability in their germ cells plus the development of biochemical genetic markers that can measure single amino acid substitutions will likely be necessary before the relationship between UDS in mammalian germ cells and repair of genetic damage can be clearly established.