Ocampo and Izpisua Belmonte ran their experiment on mouse eggs and one-cell embryos that contained mitochondria with DNA from two different mouse strains. They injected the cells with RNA designed to create endonucleases that knock out DNA from just one strain, and implanted the embryos into surrogate mothers. Tests revealed that around 60% of the mitochondrial DNA from the targeted strain had been destroyed — and the resulting baby mice were healthy.ng it.