Effect of mutagen-induced cell lethality on the dose response of germline mutations

Molecular tests for mutations require a sample of tissue From which DNA is extracted, to determine the presence or absence of one or more mutations pe r sample. To ensure mutation fixation each sample must consist of an equal number of cells that have had one or more DNA replications. In an in vivo t est, surviving stem cells compensate to give the same number of cells per s ample, leaving as the only evidence for stem cell lethality the increase in mutants of clonal origin because the mutant clone developed from a populat ion of fewer stem cells. A problem is that an increase in mutagen dose incr eases stem cell death, resulting in a decreased number of surviving target cells, thus giving a downward bias of samples with one or more mutations pe r sample. To compare in vivo tests with molecular tests we will use as a mo del system the sex-linked recessive lethal (SLRL) test For germ cell mutati ons in Drosophila melanogaster. Spermatogonia cells in male larvae were exp osed to ENU and mutations detected in sperm cells from adults. The same SLR L data were analyzed by two methods: (1) The conventional analysis of SLRL data, in which each mutation of a cluster of mutations of common origin was counted. (2) An analysis was used to simulate a sample for molecular analy sis by determining mutations per male with on equal size sample of progeny per male. With this second analysis a correction Factor is required based o n the change in cluster size of mutants of common origin. (C) 2001 Wiley-Li ss, Inc.