Figure 2. Tetraploid complementation scheme.

The diagram illustrates the process of tetraploid complementation. Wild-type embryos at the two-cell stage are recovered and subjected to electrofusion, merging the two blastomeres into a single large blastomere, effectively doubling the DNA content from 2n to 4n. These 4n embryos are cultured in vitro to blastocysts. Subsequently, ESCs are injected into the 4n blastocysts, and the injected embryos are returned to the uterus for further development. In this process, host 4n cells predominantly contribute to the formation of the placenta but have limited involvement in the embryo proper. Conversely, ESCs play a significant role in the development of the embryo proper rather than the placenta. The resulting pups are derived entirely from ESCs.