The world's first "three-parent" babies could be born next year now that the British government has given the green light to the new in vitro fertilisation (IVF) technique.
Parents at high risk of having children with a severe disability, such as muscular dystrophy, will be offered donor DNA from a "second mother" that is free of genetic defects.
Mitochondrial DNA is passed down through the mother and defects can cause problems such as heart and liver disease.
Sally Davies, the chief medical officer of England, has said the new process is the genetic equivalent of "changing a faulty battery in a car".
New regulations to allow mitochondrial DNA transfer will now be put before parliament in the UK. If they are passed, Britain will become the first European country to legalise the process and more than 100 "three-parent" babies could be born in the UK each year.
Draft regulations put forward in February were welcomed by scientists who said they would allow families to "see a little light at the end of a dark tunnel".
But the technique is controversial because it means a third party's genetic material will be passed on not only to the child but to descendants down the female line.
The guidelines state that the UK's Human Fertilisation and Embryology Authority must approve each application, and a person born through the process has no right to be told who the "second mother" was.
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