tetraploid cell

The assay starts with producing a tetraploid cell in which every chromosome exists fourfold.

The resulting tetraploid cell will continue to divide, and all daughter cells will also be tetraploid.

However, some tetraploid cells are commonly found in chromosome analysis at prenatal diagnosis and these are generally considered 'harmless'.

The tetraploid cells can form the extra-embryonic tissue (placenta etc.), however a proper fetus will rarely develop.

It is not clear whether these tetraploid cells simply tend to arise during in vitro cell culture or whether they are also present in placental cells in vivo.

The embryo will then develop normally; the fetus is exclusively derived from the ES cell, while the extra-embryonic tissues are exclusively derived from the tetraploid cells.

As with several other endocrine tumors, malignancy cannot be determined from the histologic appearance; tumors that contain large number of aneuploid or tetraploid cells, as determined by flow cytometry, are more likely to recur.

By introducing targeted mutations into the tetraploid cells and/or into the ES cells, one can study which genes are important for fetal development and which ones are important for development of the extra-embryonic tissues.