Researchers have made eggs from the cells of male mice and showed that, once fertilized and implanted into female mice, the eggs can develop into seemingly healthy, fertile offspring.

The approach, announced on 8 March at the Third International Summit on Human Genome Editing in London, has not yet been published and is a long way from being used in humans. But it is an early proof of concept for a technique that raises the possibility of a way to treat some causes of infertility or even allow for single parent embryos. “This is a significant advance with significant potential applications,” says Keith Latham, a developmental biologist at Michigan State University in East Lansing.