The influence of ploidy on the distribution of cells in chimaeric mouse blastocysts.

Previous studies of tetraploid<-->diploid mouse chimaeras and mosaics have revealed that tetraploid cells do not contribute equally to all tissues of the conceptus. In this study we have shown that, within 30 h of aggregating cleavage stage embryos, tetraploid cells were non-randomly distributed among different tissues of the early blastocyst. They were preferentially allocated to the mural trophectoderm regardless of cell size at the time of aggregation. This early effect may underlie the restricted distribution of tetraploid cells at later stages. We have demonstrated for the first time that ploidy can influence the relative position of blastomeres in the preimplantation embryo.