SEX RATIO

Abstract

Literature on the sex ratio in humans and animal species is reviewed and a series of experiments on the sex ratio in a breeding colony of rats is reported. The sex ratio (% males per 100 females) was increased to as much as 149-255 from the norm of 100.1 by increasing the interval between ovulation and insemination. Relative differences in the motility viability and aggressiveness of X- and Y-bearing spermatozoa may account for the influence of the time factor on the sex ratio. Analysis of data on 65000 dizygotic human twins indicated that about 27% more of the twins were of the same sex than of different sex in each of 3 years studied. The result is considered to be due to early and late insemination. It is concluded that the time interval between insemination and ovulation directly influence the sex of offspring.