Maternal effect on reproductive capacity of irradiated female mice.

Reproductive capacity of irradiated female mice is highly significantly strain dependent1. The num­ bers of offspring per female (after exposure to 50 R) are expressed as percentages of comparable unirra­ diated control groups and are as follows for the various strains: SEC (15%), A (18%), SEA (19%), NB (32%), and DBA (56%). The radiation-resistant DBA’s produced twice as many offspring per female as did the radiation-sensitive SEC’s (DBA: 22.5 ±1 .5 ; SEC: 11 .0±0 .7 ). This is especially remark­ able, since DBA controls produced little more than half as many offspring as did SEC controls (DBA: 40 .4±3 .7 ; SEC: 73 .4 ±0 .4 ). To determine the cause of the intraspecies variation in the radiation response of the females, crosses and backcrosses were made between the more sensitive strain (SEC) and the more resistant strain (D B A ). Virgin female mice from SEC (d se /d se ) and DBA strains, and from crosses and backcrosses be­ tween both strains, were irradiated with 0 R or 50 R of X-rays (250 kV, 15 mA, h.v.l. 0.4 mm Cu, inher­ ent filtration 3 mm Al, 80 R/min). Each group (Tables I and I I ) consisted of 26 females with the exception of the two 50-R backcross groups in which 52 females for each cross were irradiated. One day after exposure, each female was caged separately with an unirradiated C3H male for the duration of the experiment. The interval between irradiation and mating was chosen to avoid the high incidence of dominant lethal mutations induced in the first meiotic division 2. The age of the virgin females and males when first mated was 10 to 12 weeks. Females were included in the calculations if they produced one or more litters and lived longer than 30 weeks after mating. Litters were recorded and killed at