Researchers in the US have created human eggs from skin cells, a development that could transform IVF treatment.
The work at Oregon Health and Science University could help women who are infertile due to age, illness or medical treatment, as well as same-sex male couples.
The process uses somatic cell nuclear transfer, first applied in the cloning of Dolly the sheep. Scientists inserted nuclei from skin cells into donor eggs with their own nuclei removed, then fertilised them with sperm.
To reduce the chromosome count from 46 to the 23 normally present in eggs, the team used a compound called roscovitine. This triggered the eggs to discard half their chromosomes. Many of the embryos that developed had abnormal chromosome pairings.
Of 82 eggs created, fewer than 10% reached the early embryo stage and none were grown beyond six days.
The research, published in Nature Communications, is described as a proof of concept. Scientists estimate that refining and proving the safety of the method could take another decade.
