Embryos containing DNA from a man and two women have been created by scientists at Newcastle University.
They say their research, published in the journal Nature, has the potential to help mothers with rare genetic disorders have healthy children.
The aim is to prevent damaged DNA in mitochondria - the "batteries" which power the cell - from being passed on by the mother.
IVF clinics are not currently permitted to carry out the procedure.
Medical correspondent, Fergus Walsh, explains how the embryo was created.