Fly gene clue to sexual behaviour

Tweaking a single gene alters the courtship behaviour of fruit flies, a new Austrian study shows. By altering a gene called 'fruitless' (fru), the researchers, based at the Institute of Molecular Biotechnology in Vienna, bred female flies that courted other females. But altering the same gene in male flies produced insects that showed no interest in mating with flies of either sex, say the scientists, who published their findings in the journal Cell. The team stress that the factors influencing a fly's sexual behaviour are very different to those involved in human sexuality. However, the study does show that a single gene can have a dramatic effect on behaviour.

It seems that the fru gene produces two different proteins, one specific to male flies and the other to females. In two papers, the scientists report that the fru gene sets up the fly brain to produce male courtship behaviour - a series of tapping and tilting movements. Female fruit flies do not normally court at all. But female flies genetically altered to produce the male fru protein displayed the same courtship behaviour towards other females. In contrast, male flies bred to make the female fru protein did not court other flies at all.

The experiments suggest that 'switch genes' - like fru - could 'hard-wire' some fly behaviour, by switching other genes on and off. Lead author Barry Dickson said the results were 'very surprising', adding 'we have shown that a single gene in the fruit fly is sufficient to determine all aspects of the flies' sexual orientation and behaviour'. However, he also cautioned that 'in the case of humans, we know our sexual behaviours are not irreversibly set by our genes, but that doesn't mean the genes have no influence'. US biochemist Michael Weiss praised the study, saying 'the whole field of the genetic roots of behaviour is moved forward tremendously by this work'. He added that 'hopefully this will take the discussion about sexual preferences out of the realm of morality and put it in the realm of science'.