Chemical induction of presumed dominant-lethal mutations in postcopulation germ cells of mice. I. Relative sensitivity between pre- and postcopulation germ cells to isopropyl methanesulfonate.

Females from (C3H X 101)F1 and a mixed stock were injected intraperitoneally with either 25 or 50 mg/kg isopropyl methanesulfonate (IMS) or Hanks' solution 4-5 h after the midpoint of the dark period during which mating occurred. It was determined that at the time of treatment the great majority of oocytes were undergoing second meiotic division. For comparison, the same doses of IMS were given to females treated within 3-5 days prior to mating (predominantly dictyate oocytes) or to males treated within 4-5 days prior to mating (sperm in vas and epididymis). The frequencies of presumed dominant lethals induced by 50 mg/kg IMS in sperm treated in vas and epididymis, dictyate oocytes, and germ cells in mated females are 22%, 19%, and 79%, respectively, for (C3H X 101)F1 and 26%, 30%, and 76% for the other stock. Clearly, in both stocks, effects in mated females, when both female and male germ cells were treated, are relatively much higher than the added effects on dyctyate oocytes and spermatozoa. This is also true for the 25 mg/kg dose.