Chromosome analysis of early postimplantation presumptive haploid parthenogenetic mouse embryos

The chromosome constitution of early postimplantation presumptive haploid parthenogenetic mouse embryos was examined. All the embryos isolated were at the egg-cylinder stage and seven contained dividing cells. In two of the apparently healthy embryos only haploid mitoses were seen, whereas in five others an approximately equal proportion of haploid and diploid mitoses was observed. Out of 52 cells in which unequivocal counts could be made, only one contained more than the euploid number of chromosomes (mouse, n = 20). Possible reasons for the poorer development of haploid compared to diploid parthenogenetic embryos are discussed.