Although the synthetic mouse embryos bore a close resemblance to natural mouse embryos, they were not exactly the same and did not implant or result in pregnancies in real mice, according to Jacob Hanna, the stem cell scientist at the Weizmann Institute of Science who led the work.

“It’s an interesting next step, not shocking, but one that makes more plausible in the long run a proposition with broad implications: the possibility of turning any mouse cell into a living mouse,” said Henry T. Greely, a bioethicist at Stanford Law School.