Britain could become the first country in the world to permit babies to be born with three genetic parents by the end of next year.
A landmark decision by the UK Department of Health opens the door to controversial treatments for inherited diseases that make use of donated DNA from a second donor "mother".
New regulations to fertility law allowing the procedures will be issued for public consultation later this year and then debated in parliament.
If MPs find them ethically acceptable, the first patients could be treated within months.
It is envisaged that between five and ten "three-parent" babies would be born each year.
Allowing the currently illegal techniques would mark a turning point because it means, for the first time ever, altering the "germ line" made up of inherited DNA.
Experts point out that only the tiny amount of DNA in a cell's "battery packs", the mitochondria, would be changed.
DNA in the nucleus, which determines individual characteristics such as facial features and eye colour, would remain intact.
Warning over slippery slope
But some critics believe the move would mark a slippery slope leading to "designer babies" and eugenics.
The aim of the In-Vitro Fertilisation (IVF) treatments is to stamp out serious mitochondrial diseases that can be passed from a mother to her children.
Around one in 200 babies are born each year in the UK with defects in the mitochondria, rod-like bodies that supply cells with energy.
One in 6,500 is seriously affected and can suffer potentially life-threatening diseases, including a form of muscular dystrophy, and conditions leading to hearing and vision loss, heart, lung and liver problems, and bowel disorders.
An estimated 12,000 people in the UK live with the diseases.
The new techniques result in defective mitochondrial DNA (mDNA) being replaced by a healthy version supplied by a female donor.
A recent public consultation found that 56% of those questioned were "very" or "fairly" positive about the treatments. Patient focus group participants were said to be "extremely positive".
Chief medical officer Professor Dame Sally Davies said: "Scientists have developed ground-breaking new procedures which could stop these diseases being passed on, bringing hope to many families seeking to prevent their future children inheriting them.
"It's only right that we look to introduce this life-saving treatment as soon as we can."
Speaking to journalists in London, she said she personally felt "very comfortable" about altering mitochondrial DNA, even though it was part of the germ line.