London, Jan. 31: Sperm cells have been created from a female human embryo in a remarkable breakthrough that suggests it may be possible for lesbian couples to have their own biological children.

British scientists who had already coaxed male bone marrow cells to develop into primitive sperm cells have now repeated the feat with female embryonic stem cells.

The University of Newcastle team that has achieved the feat is now applying for permission to turn the bone marrow of a woman into sperm which, if successful, would make the method more practical than with embryonic cells.

It raises the possibility of lesbian couples one day having children who share both their genes as sperm created from the bone marrow of one woman could be used to fertilise an egg from her partner.

Men and women differ because of what are called sex chromosomes. Both have an X chromosome. But only men possess a Y chromosome that carries several genes thought to be essential to make sperm, so there has been scepticism that female stem cells could ever be used to make sperm.

In April last year, Karim Nayernia of Stem Cell Biology at Newcastle University, made headlines by taking stem cells from adult men and making them develop into primitive sperm. He has now managed to repeat the feat of creating the primitive sperm cells with female embryonic stem cells in unpublished work.

The next step is to make these primitive sperm undergo meiosis, so they have the right amount of genetic material for fertilisation.

Nayernia showed the potential of the method in 2006, when he used sperm derived from male embryonic stem cells to fertilise mice to produce seven pups, six of which lived to adulthood, though the survivors did suffer problems.

He is now optimistic about the prospect of lab-grown sperm from women. “I think, in principle, it will be scientifically possible,” Nayernia told New Scientist magazine. He said that he has applied for ethical approval from the university to use bone marrow stem cells from women to start experiments to derive female sperm. “We are now writing the application form,” he said.

However, Robin Lovell-Badge, a stem cell and sex determination expert at the National Institute for Medical Research, Mill Hill, London, doubts it will work: “The presence of two X chromosomes is incompatible with this. Moreover they need genes from the Y chromosome to go through meiosis. So they are at least double-damned.”