A couple is to start treatment on Tuesday to create a "designer baby" to provide a donor for their sick son.
Zain Hashmi is seriously ill
Doctors at a Nottinghamshire clinic will use pioneering IVF technology to screen embryos to find a perfect match for four-year-old Zain Hashmi, who needs a transplant.
His parents Raj and Shahana, who live in Leeds, won a Court of Appeal case which gave them the go-ahead for the treatment.
The family will know by the end of June whether the treatment has been successful.
Zain has the rare blood disorder thalassaemia and requires a bone marrow transplant.
He can be treated with blood transfusions, but over time the amount of iron in the body can build to dangerous levels.
The couple will know in June if the treatment is successful
In the absence of a donor, the couple wanted to have IVF - but use only embryos which were a genetic match for Zain.
The umbilical cord of the resulting baby would contain cells that could be transplanted into Zain.
Mrs Hashmi said: "The future is optimistic and we will always remain optimistic.
"Even when I go to bed at night I visualise Zain in his 20s, so it makes me feel I am doing something very positive for him."
The Appeal Court decision last month overturned a High Court ruling in December last year which said the Human Fertilisation and Embryology Authority (HFEA) did not have the power to license the technique under existing legislation.
It followed a challenge by
Josephine Quintavalle, of the public interest group Comment on Reproductive Ethics (Core).
But on Friday 16 May the Appeal Court judges said the ruling was a "one-off" and would not herald a genetic free-for-all.
In the future every case of its type would have to be assessed on its own merits.