Jennifer Barfield, a professor of assisted reproductive technologies at Colorado State University, clearly explains how it can come about and what led to the development of the technology that has made it possible. The key point is that in addition to the DNA that comes from the father and the mother, the fertilized egg also contains mitochondrial DNA (mtDNA) that plays a vital role in producing energy.
In 2016, a baby was born to a couple who had struggled with the consequences of mtDNA mutations that cause Leigh syndrome, a progressive neurometabolic disorder. When defective mitochondria of the woman’s egg were replaced with mitochondria from a donor who did not carry the mutation, the resulting child carried DNA from three people: the female nuclear DNA donor, the male nuclear DNA or sperm donor, and the female mitochondria donor. This was the first baby born using this technique.
Since 2016, it’s difficult to say how many of these three-parent procedures have been done and how many resulted in successful pregnancies. But with the recent birth of a baby in the Ukraine that involved three parents, many countries are now exploring if and how to use this technology. The ban in the U.S. has halted the use here but other countries have made different decisions; the U.K. has approved it.
She says that this procedure should not produce many changes.
So how much a parent is a woman who donates her mitochondria?
The short answer is not much. More than 99 percent of the proteins in your body are encoded by the DNA in the nucleus of your cells. Traits such as hair color, eye color and height, for example, are all encoded by nuclear DNA, while genes written on mtDNA are primarily related to energy production and metabolism.
Thus three-parent babies will still resemble the men and women whose sperm and egg combined to produce the 23 chromosomes in the nucleus of that first cell.
I am not sure why the US banned the procedure. There may be medical and scientific concerns that Barfield does not mention in her piece.
It is perhaps advisable to distinguish a parent from a donor of DNA. I see a parent as someone who is closely involved in a child’s upbringing. A person who adopts and lovingly cares for a child is more of a parent than someone who provides DNA but is otherwise largely uninvolved.