ONE BABY, THREE PARENTS

Nuclear DNA resides inside the nucleus of our cells. This DNA is huge, composed of reams of instructions 3.3 billion base pairs in length. Nuclear DNA comes from both our mother and father and is responsible for the vast majority of characteristics we display as we develop. However, our cells also host a small chunk of independent DNA that lives inside cellular components called mitochondria, which are energy-producing factories that power our cells. Mitochondrial DNA comes solely from our mother and is inherited from the fertilised egg cell at the beginning of gestation.

Mitochondrial DNA is miniscule in length compared to its nuclear counterpart, measuring around 16,500 base pairs in length, and contains instructions only for the function of mitochondria. In rare cases a mother can harbour a catastrophic mutation in this DNA that prevents healthy embryos developing. To circumvent this problem, scientists have developed a technique that combines nuclear DNA from two genetic parents with mitochondrial DNA from a donor. This removes the risk of inheriting mitochondrial diseases and means that the birthed baby will forever carry DNA from three people.

Three-parent babies have nuclear DNA from their mother and father and mitochondrial DNA from a donor

Embryos fertilised in the laboratory can be safely cryogenically preserved for over a decade