| Abstract: | Karyotypic and light and electron microscopical analyses were made of spontaneous preimplantation mouse parthenotes from the LT/Sv inbred strain. It was found that the activated oocyte and developing embryos were diploid. We believe that diploidization is achieved by the oogonium undergoing a premeiotic mitosis without cytokinesis followed by two meiotic divisions, thus producing diploid parthenotes. The developmental events with respect to membrane specialization, such as junctional complexes, were similar to those observed in fertilized embryos. A unique feature of the developing parthenote was the failure of the mitochondria to change during the morula stage. The mitochondria retained a few irregularly oriented cristae rather than many transversely oriented ones observed in morulae developing from fertilized eggs. The significance of this observation is discussed. |
