Though the preliminary research has raised concerns about the possibility of genetically modified babies, the scientists say that the embryos are still only primarily the product of one man and one woman.
"We are not trying to alter genes, we're just trying to swap a small proportion of the bad ones for some good ones," said Patrick Chinnery, a professor of neurogenetics at Newcastle University involved in the research.
The research was presented at a scientific conference recently, but has not been published in a scientific journal.
The process aims to create healthy embryos for couples to avoid passing on genes carrying diseases.
The genes being replaced are the mitochondria, a cell's energy source, which are contained outside the nucleus in a normal female egg. Mistakes in the mitochondria's genetic code can result in serious diseases like muscular dystrophy, epilepsy, strokes and mental retardation.