Mitochondria mean that there’s a bit more of mum in all of us
There’s another bacterial genome, or some of one, in all of our cells – but it lies in the energy-generating organelles, the mitochondria (shown above). These vital accessories are almost certainly descendants of symbiotic bacteria that colonised larger cells more than 2 billion years ago. Most of a mitochondrion’s essential functions depend on genes in the cell’s nucleus (which have been transferred there over millions of years), but mitochondria retain and use a separate genome.
When a sperm cell unites with an egg, it brings some mitochondria from your dad. These are eliminated soon after fertilisation, however, so the hundreds of mitochondria in each of your cells are descended from your mum. The unusual maternal pattern of inheritance for these few mitochondrial genes is important in studies of evolution.
Mistakes in copying the mitochondrial DNA seem more common than mistakes made when copying nuclear DNA. The mutations this causes can lead to mitochondrial diseases – an often perplexing set of conditions that can have widely varying symptoms. Not all mitochondria may be affected, and the consequences can be different in different tissues.
In the UK, the government is considering legalising an in vitro fertilisation technique for preventing mitochondrial diseases that relies on a “third parent”. This would involve transplanting nuclear DNA from the mother into an egg from a healthy donor (the extra parent) before fertilisation. The baby would have nuclear DNA from its two traditional parents and mitochondrial DNA from its third parent.Lead image:
Dr David Furness, Wellcome Images CC BY NC ND