Spontaneous and cyclophosphamide-induced sister-chromatid exchanges in diploid and endoreduplicated tetraploid metaphases of preimplantation mouse embryos

Endoreduplicated tetraploid metaphases could for the first time be induced in preimplantation mouse embryos by culture in the suboptimum medium MEM. In such endomitoses sister-chromatid exchange (SCE) frequency was approximately the same during the first and the second cell cycle. However, when morulae and blastocysts were cultured in the presence of cyclophosphamide metabolites SCE frequency was increased predominantly during the second cell cycle. Compared to diploid metaphases a decreased SCE frequency was found under both conditions of endomitoses induction, which may be related to DNA-repair processes.