シロネズミの出産回数ならびに出産年令からみた性比の変動

概要

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The present paper deals with numerical observations involving the effect of maternal age on the sex-ratio of nine strains of laboratory rats. The numerical data were derived from a total of 1100 litters containing 6889 individuals obtained during a period from 1957 to 1962. The results are outlined as follows: 1) The sex-ratio showed a general tendency to decrease with litter series (Table 1 and Fig. 1). 2) The sex-ratio tends to decrease in mothers 141-230 days old (Table 3 and Fig. 2). 3) Of the nine strains under study, the Wistar strain, Fischer-344 strain, Long-Evans strain, and Gifu-agouti strain showed a variation of sex-ratio as mentioned above (Table 2, 4 and Fig. 1, 2). From the results of the present study it is likely that the variation in sex-ratio is caused by certain physiological conditions in the mother animals.
1963-06-15