A preliminary cytogenetic study of X chromosome inactivation in diploid parthenogenetic embryos from LT/Sv mice.

We examined the replication behavior of the X chromosome in diploid 8.5- and 9.5-day parthenogenetic LT/Sv mouse embryos showing growth retardation and morphological anomalies. A single late replicating X chromosome was found in the extraembryonic as well as in the embryonic regions. However, the frequency of cells with a late replicating X was significantly lower in the extraembryonic region of the parthenotes than in that of normally fertilized embryos.