The nature-versus-nurture debate rages on, but a new study of transsexuals has shown genetics plays a key role in determining our sense of gender.

In the largest genetic study of its kind, 112 male-to-female transsexuals took part in a study involving the University of California, Los Angeles and several research organizations in Melbourne, Australia.

Researchers measured the variation in the androgen receptor gene, which is involved in the functioning of the sex hormone testosterone.

DNA samples from the transsexuals were compared with the samples from 250 typical men.

Researchers discovered the transsexuals were more likely than non-transsexuals to have a longer form of the gene.

"We think these genetic differences might reduce testosterone action and under-masculinize the brain during fetal development," Prince Henry's Institute researcher Lauren Hare said.

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