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For the production of diploid and tetraploid chimaeras with STAP stem cells, diploid embryos were obtained from ICR strain females. Tetraploid embryos were produced by electrofusion of 2-cell embryos. STAP stem cells were dissociated into single cells and injected into day-4.5 blastocysts. In the chimaera studies with both STAP cells and STAP stem cells, we did not find tumorigenetic tendencies in their chimaeras or their offspring (up to 18 months).
