DIFFERENCE IN MANIFESTATION OF THE WHITTEN EFFECT AMONG dd-GROUP-STRAINS ESTABLISHED FROM COMMON ANCESTOR, dd MICE
Strain difference in the Whitten effect was examined among 4 inbred strains (DDD, DDY, DSD and DDK) and a closed colony (ddY) belonging to the dd-group, which have been established from the common ancestor, so-called“dd mice”in Japan. Two to 4 virgin females were caged together with a male of the same strain at 60-90 days of age, and examined for copulation every morning for 10 days. The Whitten effect was evident in the DDD and ddY strains, copulation rates increased greatly on the 3rd night after male introduction. By contrast, the DSD and DDK strains showed no such effect, while about 30％ of the DDY females mated on the 1st night. These findings appear to show wide differences in manifestation of the Whitten effect by females among the dd-group-strains. Strain difference among relational strains belonging to the dd-group seems to have been fixed genetically during intense inbreeding and non-inbred closed breeding which have been continued independently since the separation.