Researchers are very close to creating sperm outside of the body for the first time.

As reported on 1 May, the feat has already been achieved with eggs. It was accomplished with cells originally derived from mouse embryos, but most experts see no reason why the technique would not work with human embryonic stem cells too. If human eggs and sperm created this way are healthy – and it is a big if – the implications for reproductive technology and regenerative medicine would be immense.

Intriguingly, eggs form from both female (XX) and male (XY) ESCs. That is because mammalian germ cells will go down the egg route unless signals produced by the testes tell the cells to become sperm.

More here.