''The creation of artificial gametes will help us understand how the real things are made, shedding light on the causes of infertility and raising the hope that sterile men and women could one day have biological children,'' she said. ''If sperm and eggs can be created from stray skin cells, people's control over their reproductive choices is dramatically altered,'' she says. Most religions would welcome ways of giving infertile men and women a possibility to produce sperm and eggs, although they might object if making gametes involved destroying human embryos, according to Donald Bruce of Edinethics, an independent consultancy in ethics and technology.
However, some scientists believe that the Y (male) chromosome is so important to sperm that attempts to use female cells will be doomed. Prof Karim Nayernia, professor of stem cell biology at the city's university, has already coaxed male bone marrow cells to develop into primitive sperm cells, and has repeated the feat with female embryonic stem cells.
He plans to apply for permission to turn the bone marrow cells of a woman into sperm.
This work raises the possibility of lesbian couples having children. Sperm created from the bone marrow of one woman could be used to fertilise an egg from her partner.
But there are some hurdles to jump, says Dr Robin Lovell-Badge, a stem cell expert at the National Institute for Medical Research in Mill Hill, London.
Prof Nayernia may have created immature, tailless sperm but they have not undergone a process called meiosis, which ensures they have the right amount of genetic material for fertilisation.
Because eggs and sperm come together to create an embryo, they need to start out with half the normal complement of genetic material each.
"The presence of two X chromosomes is incompatible with this," says Dr Lovell-Badge. ''Moreover, they need genes from the Y chromosome to go through meiosis. So they are double-damned,'' he adds.