Tetraploid complementation assay
The tetraploid complementation assay is a technique in biology in which cells of two mammalian embryos are combined to form a new embryo. It is used to construct genetically modified organisms, to study the consequences of certain mutations on embryonal development, and in the study of pluripotent stem cells.
Source: Wikipedia — Tetraploid complementation assay (CC BY-SA 4.0)