Embryonic stem cells have been turned into egg cells – the first time scientists have duplicated the process of egg formation and ovulation in the test tube.

The feat was achieved with embryonic stem cells (ESCs) from mice, but most experts see no reason why the same should not work in humans. If so, this opens the possibility that human eggs could be made in large numbers in a culture dish, instead of relying on donors.

That could advance research on infertility, the understanding of menopause and even help perfect the process of cloning, says Jose Cibelli of Michigan State University in the US. “It’s terrific,” he says. “Eggs were one of those cell types we never thought we could produce.”

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