Genetic Variation in the Timing of First Cleavage in Mice: Effect of Maternal Genotype

Eggs from female mice of eleven genotypes that had been fertilized in vivo were cultured in vitro in defined medium. The median time of first cleavage of eggs fertilized by BALB/cWt males was 24.8 h with BALB/cBy mothers and about 22 h with C57BL/6By or C57 x BALB F1 mothers. Eggs from females of seven recombinant-inbred lines had median times of first cleavage that ranged from 20.5 h in CXBI to 26.8 h in CXBJ. The timing of first cleavage bore no apparent relationship to the risk of occurrence of hermaphrodite offspring, which also differed between the recombinant-inbred lines. When mated to SJL x SWR F1 males, which never produce hermaphrodite offspring, BALB x C57 F1, CXBH, and SJL x SWR F1 females produced eggs that cleaved at different times, but in all cases earlier than eggs of the same genotype fertilized by BALB/cWt males. Fertilized eggs from CXBJ females often underwent first cleavage successfully but failed to develop further in culture. Almost all eggs from females of the other genotypes formed blastocysts successfully. Eggs that had completed first cleavage were somewhat less likely to form blastocysts if they had been fertilized by a BALB/cWt male than if they had been fertilized by some other male.