The UK looks set to become the first country to allow the creation of babies using DNA from three people, after the government backed the IVF technique.
It will produce draft regulations later this year and the procedure could be offered within two years.
Experts say three-person IVF could eliminate debilitating and potentially fatal mitochondrial diseases that are passed on from mother to child.
Opponents say it is unethical and could set the UK on a "slippery slope".
They also argue that affected couples could adopt or use egg donors instead.
Mitochondria are the tiny, biological "power stations" that give the body energy. They are passed from a mother, through the egg, to her child.
Defective mitochondria affect one in every 6,500 babies. This can leave them starved of energy, resulting in muscle weakness, blindness, heart failure and death in the most extreme cases.