The creation of IVF babies with DNA from three parents to be allowed by Britain on Tuesday in a move that has divided the campaigners and religious leaders. Britain could become the first country in the world to allow this.
Lawmakers in parliament are set to vote on mitochondrial DNA donation techniques aimed at preventing serious inherited diseases.
Mitochondrial DNA (mDNA) is passed on through the mother. Mitochondria supply the energy inside cells.
Hereditary mitochondrial diseases affect major organs and cause symptoms ranging from poor vision to diabetes and muscle wasting.
Under the proposed change to the laws on in-vitro fertilisation (IVF), as well as receiving normal "nuclear" DNA from its mother and father, the embryo would also include a small amount of healthy mDNA from a woman donor.
The vote has split opinion between experts supporting the idea and opponents who fear it would be the first step on the road to "designer" babies.
Members of Parliament are to hold a 90-minute debate on whether the laws on IVF should be amended to allow babies to be conceived with genetic material from three individuals.
At the end of the debate, MPs have a free vote on the issue, meaning they can vote according to their conscience and are not forced to vote along party lines.
Experts believe that the use of mDNA from a second woman could potentially help around 2,500 women in Britain at risk of passing on harmful mDNA mutations.
IVF pioneer Lord Robert Winston told The Daily Telegraph newspaper that the procedure was no more sinister than a blood transfusion.
International charities have written an open letter to MPs urging them to back a change in the law, saying it "offers families the first glimmer of hope that they might be able to have a baby that will live without pain and suffering".
Meanwhile Doctor David King, director of the watchdog group Human Genetics Alert, said: "Advocates say we shouldn't worry about 'slippery slopes'. Yet in my experience, they are the very same people who, a few years later, push us to take the next step and the one after that."
"If we want to avoid the nightmare designer baby future we must draw the line here."