Britain’s House of Commons voted Tuesday 382-128 to allow the creation of babies from three people—sort of. The technique concerns mitochondrial DNA, which governs energy production in cells and is only passed on by the mother. Defective mitochondria can lead to organ failure, blindness, and epilepsy. About one in 5,000 children in the U.S. inherit a defective one. The technique allows a woman to donate her healthy mitochondria to the mother’s DNA, which fixes the energy problem but keeps the other 99.99 percent of genes untouched. That egg is then mated with male sperm in IVF. The British House of Lords must approve the measure before it becomes law.