Sex Ratio in Mouse Chimeras Derived from Aggregation of Five Bisected Embryos

Abstract

In vitro development of chimeric mouse embryos produced by aggregating five bisected 8- or 10-cell embryos and sex ratio of fetuses developed from the aggregated embryos were investigated. Twenty-eight to 30 hours after start of culture, 198 of 202 aggregated embryos (98.0%) developed into single morulae or blastocysts. The morulae or blastocysts were transferred into the uteri of psuedopregnant recipients. Eighteen of 21 recipients (85.7%) became pregnant. The recipients were autopsied on the 19th day of pregnancy. One hundred and eighteen of 185 transferred embryos (63.8%) had implanted and 77 (41.6%) had developed into live-normal fetuses. Sex of the fetuses was determined by the gross observation of the gonad. Fifty of 78 fetuses including one which had died during late pregnancy were classified as male and 27 as female. Remaining one could not be classified as male or female, because it had a testis on the left and a flat testis-like gonad on the right. Mean body weight of live fetuses was 1.34g, and males (1.39g) were significantly heavier than females (1.25g, p⟨0.05). On the basis of these results, the relationship between sex chromosomal constitution and gonadal differentiation in mouse chimera was discussed.