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 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 10 "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.
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 which 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".
Experts in the field are also behind the procedures, which are being actively developed at a new laboratory in Newcastle funded by the Wellcome Trust.
Draft regulations making the UK the first country in the world to offer the treatments to women with a family history of mitochondrial disease will be published later this year, the Department of Health said.
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.
"What we're going to do now is start to develop the regulations, to consult on the regulations, and then to take them into Parliament."
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.
"I do think quite carefully about ethics, I always did as a clinician and I still do, perhaps because my father was a theologian," she said.
"I am comfortable with this. I think we will save some five to 10 babies from being born with ghastly disease and early death without changing what they look like, or how they behave, and it will help mothers to have their own babies."
She compared mitochondria to the battery in a car and the nucleus to the driver.
Mitochondrial replacement treatments were analogous to a driver abandoning a car with a dud battery and switching to a vehicle whose battery functioned properly.
Two mitochondrial replacement procedures have been explored by scientists. One, pro-nuclear transfer (PNT) involves removing an early "pronucleus" containing parental DNA from a fertilised egg which has not yet had a chance to develop into a multi-cell embryo.
The pronucleus is transferred to a fertilised egg whose own pronucleus has been removed and which contains healthy mitochondria.
The donor egg grows into an embryo and baby possessing nuclear DNA from its mother and father, and mitochondrial DNA from the donor.
Maternal spindle transfer (MST), the second technique, has a similar outcome but is carried out before fertilisation. A spindle-shaped structure containing a mother's nuclear DNA is first removed from one of her eggs. This is transplanted to a donor egg which has had its own spindle removed, and is then fertilised by the father's sperm.
Under current law, such procedures are banned because any tampering with inherited genetic material is illegal.
However a safeguard has deliberately been left in the Human Fertilisation and Embryology Act allowing this blanket rule to be changed by Parliament in exceptional circumstances.
Dame Sally said: "There are clearly some sensitive issues here, but.. it's clear there is general support to allow these treatments subject to strict safeguards. So what we're going to do is move forward."
She made it clear that the outright ban on altering nuclear DNA would remain in place and there was no likelihood of that position changing "in the foreseeable future".
Josephine Quintavalle, from the group Comment on Reproductive Ethics (Core), said the proposals were already causing worldwide concern.
"This controversial announcement - presented simply as innovative genetic treatment when it is in effect an endorsement of highly contentious germ line modification of the human embryo - is hardly unexpected, given the enthusiasm already shown by both the Nuffield Council (on Bioethics) and the HFEA.
"Our focus now turns to Parliament where we hope that the proposals to create three-parent embryos will be voted down, and research and investment will be directed towards internationally approved ethical solutions to mitochondria disease, without any manipulation of the human germ line."
Former Lib Dem MP and health spokesman Dr Evan Harris, who began the campaign to legalise mitochondrial replacement treatments in 2007, said: "Any delay in the final regulations being voted on by Parliament could delay the ability of those who need this treatment to get it and risk the UK's world-leading research and medical expertise in this area.. going abroad. So this welcome progress will ultimately be judged by patients and their doctors on the speed at which the law change is made - preferably early next year."
Dr David King, director of Human Genetics Alert which strongly opposes the treatments, said: "These techniques are unnecessary and unsafe and were in fact rejected by the majority of consultation responses.
"It is a disaster that the decision to cross the line that will eventually lead to a eugenic designer baby market should be taken on the basis of an utterly biased and inadequate consultation."