Abstract
The sex-determining theory which Geddes and Thompson 1 and others attribute to Girou, namely, that the better nourished parent tends to determine the same sex in the offspring, was tested by mating rats fed diets adequate or high in protein (containing 30% to 50% casein) with rats fed diets low in protein (containing 7.5% to 12% casein, but otherwise similar to the high protein diets). Albino, hooded and hybrid (hooded-albino) rats were used. When increases in weight suggested pregnancy, the females were isolated and placed on a stock diet. The sex of the offspring was determined within 24 hours after birth. A preliminary study which lasted 8 months during which 49 litters were obtained yielded some data supporting Girou's theory but needing further confirmation. Accordingly a further study was undertaken which thus far involved 15 months during which 652 litters were obtained.
In our main study, only one male was used for mating with the females in each of 7 groups including from 10 to 17 individuals. Thus we obtained from 52 to 126 litters from each male within a year. Genetic variables were also reduced to a minimum by using the same females repeatedly for mating when possible but rotating them in random order between the different groups, excepting that albinos were mated only with albinos and hooded with hooded rats. Between Nov. 10, 1937, (the beginning of our main study) and Feb. 8, 1938, we obtained, from matings of low protein males with normal and high protein females, 51 litters (av. 8.2 young per litter) including 217 males and 203 females and yielding a sex ratio of 107 (males): 100 (females). During the same period, we obtained, from matings of normal and high protein males with low protein females, 64 litters (av. 8.6 per litter) including 327 males and 226 females and yielding a sex ratio of 145:100.
Get full access to this article
View all access options for this article.