Effects of mutagenized X chromosomes of Drosophila melanogaster on viability and fitness in males.

Drosophila melanogaster males were treated with different doses of X-rays or ethyl methanesulfonate (EMS) and mated so that mutagenized X chromosomes could be recovered and tested for lethal mutations and for less drastic mutations affecting viability and other aspects of fitness. The lethals were detected in standard X-linked lethal tests. The less drastic mutations were detected in one generation tests for effects on viability and in multigeneration tests for effects on overall fitness. The Poisson-corrected frequencies of the lethal mutations increased linearly with dose for both X-rays and EMS. Based on the data, 1 Krad X-rays given acutely induces the same number of lethals as 0.55 mM EMS administered by feeding. For some of the X-ray and EMS doses, the mutagenized chromosomes that were nonlethal reduced the viability of their carriers by a small amount, but there was no discernable dose-effect relationship. However in every case where a viability effect was seen, the percentage reduction was less than the corresponding frequency of lethals. All the groups of mutagenized nonlethal chromosomes reduced overall fitness by a significant percentage. Wherever a meaningful comparison was possible, this reduction was 2-3 times the reduction in viability, but, as in the viability data, no dose-effect relationship was discernable.