Abstract
This experimental investigation was to seek a possible approach for understanding the changes of prenatal sex ratio. By making use of female mice, the sex ratios of embryos were established as 98. 3, 109.5 and 111.7 on 3. 5, 10.5 and 18.5 days of gestation, respectively. There were no significant differences among these ratios. No deviations from the 1:1 theoretical ratios were also observed except for the ratio at perinatal stage. But, it was found that a slight excess of male embryos was consistently evident after the mid-term of gestation. From the findings of reproductive performances at each gestational stage, it was suggested that the selective mortality at implantation might play an important role on the change of the prenatal sex ratio in mice. From an epidemiological point of view, the use of an animal model is a relevant tool, so far as we comprehend the differential characteristics between man and other mammals.
