The First Polar Body Can Be Used for the Production of Normal Offspring in Mice

The purpose of this study was to determine whether chromosomes in the first polar body can participate in normal embryonic development. In the mouse the majority of first polar bodies degenerate soon after ovulation, but a few remain viable for 10 h or more. When the contents of a live polar body were injected into an enucleated mature oocyte and examined 2 h later, the polar body chromosomes were arranged on a metaphase plate as seen prior to the secondary meiotic division. Such oocytes were fertilized normally by sperm injection. When 2-cell embryos were transferred to foster females, 30-57% developed into fertile offspring. This outcome supports a long-standing belief that chromosomes ejected into the first polar body have the same genetic potential as those remaining in the oocyte after the first meiotic division. As the chromosomes in the second polar body are known to have full potential to participate in normal embryonic development, it is theoretically possible to reproduce four offspring by using chromosomes in one oocyte.