MPs vote today on whether or not to allow “mitochondrial DNA transfer”, which would allow would-be mothers with unhealthy DNA to use material from a second woman. What does it involve?
Calling children conceived using mitochondrial DNA from a female donor "three-parent babies" is a bit of a stretch.
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.
Getty Images/iStockphoto
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."
Mitochondria used to be bacteria.
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.
Getty Images/iStockphoto
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."
