[Cytological study of spontaneous embryonic mortality before implantation in mice of different genotypes].

Spontaneous preimplantation embryonic mortality was studied cytologically for mice of different strains and their combinations. It was found that this index was determined to a considerable extent by the genotype. Its level varied from 5 to 10% depending on the genotype. The stoppage of embryos' cleavage and, probably, their death occurs mostly at the stage of 2-12 blastomeres.