How a child can have DNA from three people

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.


  1. says

    There are, of course, moral and ethical reasons to ban this.

    First and foremost, it inherently screws over every child waiting for a forever family.

    Instead of playing god and fiddling with genes, we need to actively promote adoption, and stop with this stupid, selfish insistence that a family is only “real” if one parent gestated and birthed the child.

  2. Holms says

    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.

    Most likely USA’s phobia of anything that resembles ‘playing god’ to the religious majority.

    It’s also worth noting that mtDNA is much more conserved / much less variable between individuals; the basic chemistry of metabolism places relatively tight constraints on that.

    People get to make choices about their bodies, and medical technology is there to help them do that. Hopefully adoption was presented to those parents as an option, but they get to make that decision.

  3. Callinectes says

    @1 As much as permanent adoption needs to increase, especially with older children, even with perfect adoption rates there are not enough children available to every couple with fertility issues. This is especially so for parents who want to raise children from babies.

  4. agender says

    To me mtDNA transfer seems to be the most uncontroversial of the genetic technologies, because I remember a caution that the egg donor (who also gives most mitochondria) and the female DNA-donor have to be quite closely related. There was a risk that the diseased mitchondria took over when they were not.
    (Sorry, I have too little computer time today to find the articles -- one on bbc and something in a journal -- a.f.a.i.k I can remember inside a paywall)
    It is not that one -- but from what I can glimpse it has this caution in it.

    And c3, Callinectes -- far from it TODAY. there are lots and lots of born unwanted´ s (maybe the birthmachines are still not used to complaining -- my existence is enforced by a still existing abortionforbidding law; I speak from experience).
    But in a better future without abortionforbidding laws this could be.

  5. says

    I met a guy who had a complete bone marrow replacement due to cancer. If I understand it right he had 2 set of DNA -- a blood test would give different results than an epithelial cell sample.

  6. Reginald Selkirk says

    This has personal impact for me. A relative of mine had a child with Leigh syndrome. The child died within a year or so, and the experience caused much suffering to the parents.

    As a biologist, I will note that not all genes involved in mitochondrial energy production are found in the mitochondrial chromosome. A lot of them have migrated to the nucleus over evolutionary time.

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