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What is being proposed?
Scientists are working on a way of transplanting the nucleus of a fertilised egg - containing most of the genetic information for the resulting child - into an unfertilised egg that has had its nucleus removed. This egg would be donated by another woman - hence the creation of a child with three genetic parents.
Why do scientists want to do this?
Scientists at Newcastle University say they have already created three-parent embryos.
There are certain diseases which are passed down via the egg cell from mothers to their children. Scientists want to use this procedure to eliminate this risk.
What does the procedure involve?
Certain diseases are caused by faults in parts of a cell called mitochondria. These are found in the area of a cell around the nucleus, and are sometimes described as the "power packs" inside the cell that produce the energy it needs to function.
The mitochondria found in egg cells can be passed on to a child, but the mitochondria of sperm cells cannot. Therefore faulty mitochondria can only passed on by the mother.
To avoid this, an embryo would be created through IVF treatment using an egg and sperm from a couple at risk of a mitochondrial disease. A second egg, taken from a women without any mitochondrial defect would then have its nucleus removed.
The nucleus from the couple's embryo would be inserted into the donated egg, producing a new embryo with genetic material from all three parents that could be allowed to develop into a child.
What are the objections?
Josephine Quintavalle is one of many who have spoken out against embryo experiments.
Research into the procedure results in the destruction of human embryos. As Josephine Quintavalle of Comment on Reproductive Ethics has said, "It is human beings that they are experimenting with."
There could also be serious psychological implications for a child born with three genetic parents. The media has covered numerous cases where egg or sperm donors later stake a claim on the interests of the child they helped to produce, and the same could well happen here. The law in this area is unclear.
The role of mitochondria in a child's development is not fully understood. Though the transfer of mitochondria might be beneficial in eliminating one disease, it could introduce new problems that might not become apparent until the child is older, or could present themselves in future generations.
What does the law say now?
As at 5 February 2008, scientists can carry out research using this kind of technique if the Human Fertilisation and Embryology Authority (HFEA) grants them a licence.
However, this permission is limited to research only. The embryos must be destroyed on their fourteenth day of development, and cannot be implanted.
Could the law change?
Some scientists would like the Human Fertilisation and Embryology Bill to give the HFEA powers to permit the creation of three-parent families.
Currently (5 February 2008), the Bill contains a regulation-making provision to allow the Secretary of State to give the HFEA these powers at some stage, provided the consent of both Houses of Parliament is given.
The Government has indicated that the issue needs further consultation and that regulations will be introduced as soon as possible.
Latest briefing on the embryos Bill