Providing insight into the sometimes mysterious biology of reproduction, researchers in Japan have identified a gene that controls whether the reproductive precursor cells known as germ cells eventually become sperm or eggs.

The scientists described experiments on a small fish called the medaka, or Japanese rice fish, that revealed the role of a gene called foxl3 in controlling the fate of germ cells.

Germ cells are present in the bodies of vertebrates of both sexes, but the molecular mechanism that drives them to develop into either sperm or an egg has been elusive.