6 Things You Didn't Know About "Three-Parent Babies"

MPs have voted in favour of "mitochondrial DNA transfer", which will allow would-be mothers with unhealthy DNA to use material from a second woman. What does it involve?

UPDATE: the House of Commons has voted in favour of the measure.

A total of 382 MPs voted for it, while 182 voted against. However, would-be parents will not be able to undergo the procedure until it is approved by the Human Fertilisation and Embryology Authority (HFEA).

1. Calling children conceived using mitochondrial DNA from a female donor "three-parent babies" is a bit of a stretch.

Getty Images/iStockphoto

The DNA you think of as making you "you" – the stuff that makes your eyes brown or blue or your hair straight or curly, the stuff that means you can curl your tongue or gives you a dimpled chin – isn't touched. That's the DNA in the nucleus of your cell (the pink thing in the picture above), which consists of 46 X-shaped segments called chromosomes, or 45 X-shaped ones and one Y-shaped one if you're a boy.

What is replaced in "three-parent babies" is the DNA in our mitochondria, tiny little "organelles" within the cell that provide energy – they're often called the "powerhouse of the cell", or the battery. They're the bits in red in the picture above.

There are more than 20,000 genes in your nuclei. By contrast, there are 37 in your mitochondria, and the two don't ever mix.

2. Mitochondrial disease can be horrible, and this procedure could prevent it in children.

There might not be many genes in the mitochondria, but when they go wrong, it can be devastating. Mitochondrial disease can lead to diabetes, blindness, deafness, learning difficulties, muscle wastage, and early death. The battery in your car may not the most important bit, but when it goes wrong, the car won't start.

And because the mitochondria are present in every cell – all 100 trillion or so in the body – it is impossible to replace them, except right at the moment of conception.

Sarah Wollaston, a Conservative MP and medical doctor, told BuzzFeed News: "This isn't about wanting a child who's more intelligent, more beautiful, has a particular eye colour or a different kind of personality. This is about trying to save children from a really hideous disease."

3. Mitochondria used to be bacteria.

Getty Images/iStockphoto

Lynne Margulis, a biologist, suggested in the 1960s that mitochondria used to be free-living bacteria and joined forces with the cells of our ancestors about 2 billion years ago. This is now the accepted hypothesis. For one thing, it explains why mitochondria have DNA of their own.

4. If MPs vote in favour of allowing the technique today, Britain will be the first country in the world to have approved it explicitly.

Other countries have laws that could allow this sort of treatment – the USA doesn't specifically ban it, for instance, although it would be unlikely to get past the health regulator. Lots of other countries have lax or non-existent laws on this subject. But Britain will be the first country to have had a proper parliamentary debate to decide whether science, ethics, and public opinion is behind the move. And in all likelihood we will then be the first country to go ahead with it.

We've been pioneers of technology like this before – specifically in vitro fertilisation, or IVF. Louise Brown, the first "test tube baby" (actually conceived in a Petri dish), was born in Oldham to a couple who'd been trying to conceive for nine years.

Now, about 50,000 women have IVF in Britain every year, and it is estimated that the procedure has led to 5 million births worldwide. That's a lot of happy families that otherwise wouldn't have existed.

"Decades ago there was a hugely controversial debate [over IVF], and a lot of the same issues were raised, but would we really want to reject IVF now?" said Wollaston. "Of course I understand there are people who feel profoundly that anything that involves a kind of genetic manipulation would be part of a slippery slope. But there's always going to be a first time for using this technology, and this has been debated now for seven years."

5. Mitochondrial DNA is only passed down through mothers.

Getty Images/iStockphoto

Sperm are tiny little things. The competition between them is so ruthless that there's no spare capacity: A sperm is just a powerful swimming tail and a sort of genetic warhead stuffed with DNA. But eggs are much bigger, and contain the equipment required to build a new human – not just (half) the nuclear DNA, but all the rest, including mitochondria.

That means it is possible to trace female ancestry back using mitochondrial DNA, which, even as the nuclear DNA is mixed and chopped and changed, remains the same – barring mutations – throughout the generations. It was using mitochondrial DNA that scientists were able to discover when and where the woman who is the most recent common ancestor of all modern humans lived. "Mitochondrial Eve" (as she's known, although she wasn't the first woman to have lived) was probably born between 100,000 and 200,000 years ago, in east Africa.

6. A yes vote in parliament would not mean the procedure starts taking place immediately.

There are understandable concerns over the risks of any new procedure, especially ones involving babies. But as Mark Henderson, head of communications at the biomedical charity the Welcome Trust, told BuzzFeed News: "There are uncertainties, as with any new treatment. But the risks are generally considered by scientists to be low, certainly compared to the known risks of having a child with mitochondrial disease."

More importantly, he said, a yes vote would not mean the end of scrutiny. Parliament is voting on the general direction of travel, informed by the science and public opinion, and would then hand over detailed regulation of the science to the Human Fertilisation and Embryology Authority (HFEA). The HFEA would look at the state of research and say whether or not the procedure is safe yet to carry out on humans. It could be that it says more research is required. Parliament will not be required to vote again, but until the HFEA is satisfied, no "three-parent babies" will be born.