The discovery of a single gene which controls gender could pave the way for simpler treatment of trans people.

Researchers at the National Institute for Medical Research discovered that just one gene prevents females from developing male physical characteristics such as facial hair and testes.

The study in adult mice showed that when the gene, known as FOXL2, was artificially switched off, the ovaries of female mice began developing into testes and they produced male amounts of testosterone.

Previously, it was thought that gender was controlled by X chromosomes and Y chromosomes. Men typically have XY, while women have XX. This study refutes the consensus that gender is fixed at birth and that embryos are female unless they possess a male-determining gene.

The paper was published today in journal Cell.

Co-author Robin Lovell-Badge said: “We take it for granted that we maintain the sex we are born with, including whether we have testes or ovaries. But this work shows that the activity of a single gene, FOXL2, is all that prevents adult ovary cells turning into cells found in testes.”

According to the Independent, he added: “If it is possible to make these changes in adult humans, it may eventually remove the need for surgery in gender-reassignment treatment.

“If this does become possible, it’s likely that while treated individuals would make the right hormones for their new sex, fertility would be lost.

“It’s still very speculative, but it’s possible that this approach could produce an alternative to surgery and the removal of gonads – ovaries and testes. It’s a little more natural, but of course anyone undergoing such a sex change would be infertile.”

Professor Mathias Treier of the University of Cologne in Germany described the results as “spectacular”, saying that researchers had only expected the female mice to stop ovulating.

Although the outward appearance of the mice did not change during the experiment’s timescale, Treier said the ovary cells began changing within 48 hours after the gene was switched off.

The new testes did not produce sperm but the presence of testosterone suggests that in humans, this could lead to facial hair, a deeper voice and increased muscular mass.

Although research in humans is a long way off, researchers believe this could eventually spell a end to lengthy gender reassignment treatment which currently uses hormones.

Lovell-Badge said that researchers were now trying to discover whether male cells could be turned into female cells.

Other possible applications for the findings include treatment for early menopause in women.