Same-sex couples may one day be able to have babies who are genetically related to both partners, thanks to a scientific breakthrough.
The newly developed process, called IVG (In Vitro Gametogenesis), also opens up the possibility for babies to be conceived using the DNA of just one parent - or three-or-more parents.
Sonia Suter, from George Washington University, America, has written about the technique in the Journal of Law and the Biosciences.
"This technology would allow same-sex couples to have children who are biologically related to both of them," Suter explained.
IVG could allow babies to be born with 50% of their DNA from each partner in a same-sex couple
"[The technique would also] allow single individuals to procreate without the genetic contribution of another individual," Suter added. "And facilitate 'multiplex' parenting, where groups of more than two individuals procreate together, producing children who are the genetic progeny of them all."
"IVG also presents the possibility of ‘perfecting reproduction’, by greatly improving the ability to screen for undesirable diseases or even traits."
If IVG is approved as "a safe and effective method of human reproduction IVG", Suter explains, it would involve scientists collecting a somatic cell (such as a cell from a muscle) belonging to each parent.
These cells could be used to produce a stem cell from which gametes (sex cells) would be derived. These gametes could be used to produce an egg cell from a man, or a sperm cell from a woman.
Suter writes: "For same-sex couples this produced gamete could be combined with a ‘naturally’ derived gamete from the other member of the couple to produce an embryo. The resulting child would share 50% of its genome [DNA] with each member of the couple."
For straight couples with fertility problems that mean one or both partners cannot provide sperm or an egg, IVG would also allow them to reproduce without relying on egg or sperm donation from a third person.
With "multiplex" parenting among four parents, Suter explained, sperm and eggs made from stem cells would be taken from each adult, and they would be combined in two pairs to create two embryos. Cells would then be taken from each of these embryos to create further gamete cells to be combined to make a third embryo. This embryo would have a quarter of DNA from each parent.
For "solo IVG", involving just one parent, Suter adds: "the individual would derive the female or male counterpart of gametes via IVG to use with his or her naturally derived gamete to produce an embryo through IVF."
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So far the technique has only been trialled on mice but according to Suter, "research on human cells suggests that IVG with reproductive potential may one day be possible with humans."
Suter flags up that while IVG may be "preferable" to other fertility treatments in some circumstances, in others it could be "substantially more problematic".
For instance, in the case of "solo IVG" all of the baby's genetic material would come from one person's DNA, which could lead to greater "safety challenges".
Other fertility experts have echoed concerns about IVG.
Professor Geeta Nargund, Medical Director of CREATE Fertility told HuffPost UK Parents: "This comment from Prof Suter is pure speculation. We are not close to a position where IVG in humans is a scientific reality.
"There are numerous ethical, scientific and safety concerns to be overcome before we can consider this as a possibility"
Dr Helen Webberley, GP for Oxford Online Pharmacy added: "While scientifically, this is very exciting and indeed opens up possibilities for same sex couples or single parents; socially and morally it does throw up an awful lot of concerns.
"There is so much more to creating a child, that will go on to become a functioning adult, than just contributing DNA.
"As a doctor I see children in real difficulties when their home life is not congruent and harmonious, and it can cause immense problems to the developing brain.
"Fertility is closely governed in the UK by the Human Fertilisation and Embryology Authority and I trust them to consider all aspects of developments such as these."
Tommy’s midwife, Kate Pinney said: "We support any positive progression in supporting and helping infertile or same sex couples to have their own biological children.
"However there are extensive ethical and moral concerns that need to be fully explored and considered before this can become a reality."
Dr George Ndkwe, medical director of the Zita West fertility clinic, said he's been following the development of this technique for quite some time.
"This is wonderful science, but it's going to raise questions," he said.
"There are possible uses of it, which in my opinion can be useful. For instance, for somebody who has no sperm at all or a woman who has no egg, if you can use any of their cells to create sperm or eggs then they can have treatment, so to use it in that way specifically for treatment, in my opinion may have some benefits.
"But with this IVG technology you're able to create a large number of eggs and sperm, so a problem arises if it is used to select traits in babies. There's a danger there.
"Another problem, is that when we begin to talk about 'multiplex parenting', where you can get the desirable genes from say 20 people. I think that's going to become a problem because if you add the DNA from 20 different people, then who is the parent?
"It would completely challenge our notion of parenthood with very complex legal implications. That's where it gets very scary."