Altered sex ratio of live young after transfer of fast‐ and slow‐developing mouse embryos

We cultured eight‐cell mouse embryos to blastocyst stage, divided them into three groups according to the time of blastocoel formation, and transferred them separately into recipients. The proportion of live young from the fast‐developing embryos was slightly high (49%) but not significantly different from those of other embryos (38% and 39%). However, the sex ratio of live young from the fast‐ and slow‐developing embryos was significantly shifted toward the male (71%) and to the female (80%), respectively.