Effects of preovulatory overripeness of primary oocytes were studied cytogenetically in 2-cell rat embryos which developed from the ova unduely aged for 48 hours in mature follicles. Both aneuploids and mosaics increased significantly in the experimental group. It was clearly indicated that the delayed ovulation induces nondis j unction and anaphase lag of chromosomes during both the meiotic and first cleavage divisions. A significant increase of polyploidy was also proven as the result of the delay in ovulation. Its causal mechanism was confirmed to be polyspermy.
In order to assess the syntenic relationship of genes in the laboratory rat (Rattus norvegicus) and mouse (Mus musculus), rat gene mapping is undertaken in rat-mouse somatic cell hybrids with the rat chromosome segregation. The genes coding for adenylate kinase-2 and phosphoglucomutase-2 are syntenic with enolase and phosphogluconate dehydrogenase, and assigned to rat chromosome 5. The four genes are syntenic in man and mouse, suggesting the conservation of the linkage relationship of homologous genes in the three divergent species.