Previous studies of tetraploid <----> diploid mouse chimaeras and mosa
ics have revealed that tetraploid cells do not contribute equally to a
ll 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 regardle
ss of cell size at the time of aggregation. This early effect-may unde
rlie 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.