Abstract
Sex ratios in rats were studied among 12, 492 animals of the Wistar-Imamichi strain which were born at Dr. Imamichi's Laboratory of the Nippon Veterinary and Zootechical College in 1969 and 1970. Analysis on sex ratio was performed by the same method as described in a previous report and used to determine swine sex ratio3). The classes which showed a shift of sex ratio to either sex were cited mainly in tables. The results obtained are summarized as follows.
Total sex ratio (Table 1): In a total, the sex ratio was 49.2%. It cannot be said that three was any significant shift of sex ratio to either sex even at 5% level.
Paternal or maternal individuals (Table 2): Of the paternal individuals obserbed, only three individuals gave rise to a shift of sex ratio to female in their offspring.
All the maternal ones obserbed, however, showed a shift of sex ratio to either sex.
Litter series (Table 3): A shift of sex ratio to female (significant at 5% level) was seen in one class (litter series 2). When the litter series were grouped, however, no shift of sex ratio was noticed at all.
Litter size (Table 4): In one class (litter size 7), a shift of sex ratio to female (significant at 1% level) was recognized. When the classes of litter size were grouped, however, no such shift was seen at all.
Season (Table 5): Both secondary and primary sex ratios in winter were significantly low at 1% level. When analyzed annually, sex ratio was significantly low at 1% level. When analyzed annually, sex ratio was significantly low in the winter of 19691970 (from December, 1969, to February, 1970). There was a significant difference in secondary sex ratio between winter and any other season, and one in primary sex ratio between winter and spring, and winter and summer.
Age of parents (Table 6): No shift of sex ratio was seen in any group of paternal or maternal age, or any group of age. A significantly low sex ratio, however, was observed in one age group (one month superior in peternal age to maternal one).
Annual sex ratio (Table 7): No annual shift of sex ratio was noticed during two years in the present study.
