Haploid mouse embryos obtained by microsurgical removal of one pronucleus.

A pronucleus can be microsurgically removed from the fertilized mouse egg. Out of 145 haploid eggs obtained by this method and transplanted into the oviduct of pseudopregnant recipients, 36 multicellular embryos were recovered on the 4th or 5th day. On the 4th day all embryos were morulae composed of 8-50 cells, with the majority containing 8-16 cells. After an additional 24 h in vivo or in vitro the cell number increased considerably, sometimes up to as many as 80. Out of 36 multicellular embryos only one developed into a blastocyst while the others remained at the morula stage. Karyological investigations confirmed that the embryos were haploid and revealed that all were gynogenetic. Possible reasons for the absence of the androgenones and for the scarcity of blastocysts are discussed.