Male flies to male
IS HOMOSEXUALITY in the genes? Researchers at the National Institutes of Health (NIH) in Bethesda, Maryland, USA, report that a single gene transplanted into fruit flies made the males show homosexual behaviour. This display of homosexuality is interesting to scientists because a gene similar to that transplanted into the fruit flies exists in human beings.
Biologists Ward Odenwald and Shang-Ding Zhang found that the male fruit flies with the transplanted gene formed groups, linking together end-to-end in big circles or in long winding rows, and rubbed their genitals with each other.
The behaviour was baffling because fruit flies are sexually highly active creatures. If a male and a female fruit fly are put in a bottle, they will produce a new generation in as little time as 2 weeks. In fact, this trait of the fruit flies has made them popular with genetic researchers who are usually interested in observations covering sevtral generations of a species.
But Odenwald and Zhang found that the transplanted gene does not make the males renounce heterosexuality altogether. The researchers observed that if a male fly with the transplanted gene is surrounded by females, he will readily oblige by fertilising them. This implies that the gene induces bisexual rather than homosexual behaviour. However, no unusual behaviour is observed when the gene in question is transplanted into female flies.
The DNA (deoxyribonucleic acid) section of fruit flies that causes the aberrant behaviour is called the "white gene" because when it undergoes a particular type of mutation, it causes the normal red eyes of fruit flies to turn white.
An important function of the "white gene" is to produce a protein that enables cells to utilise tryptophan, which is an essential amino acid, present in the blood. If the gene fails to perform this function, then the red eye pigment cannot be formed.
Normally the "white gene" is present only in some cells - which include the-brain cells - of the fruit flies' bodies. But the researchers inserted the normal version of the gene in such a way that it got activated in every cell. This resulted in complete mayhem in the flies' life.
As every cell sucked in tryptophan from the blood, a paucity of the amino acid developed in the brain. The altered levels of tryptophan in different parts of the insects' bodies triggered off other reactions.
A consequence was that less serotonin - a substance that transmits impulses between nerve cells - was made by the brain. Abnormal levels of serotonin in humans cause extremes in behaviour from depression to violence. In the case of male fruit flies, the researchers believe that a shortage of serotonin might have led to the homosexual behaviour. Meanwhile, gays have, by and large, welcomed the study as it projects homo-sexuality as a trait, like skin colour, rather than a lifestyle preference. But some others feel that the research sees homosexuality in the male fruit flies as unusual behaviour, making it seem like a "defect" that needs to be corrected.
Says Martin Duberman, head of the Center for Lesbian and Gay studies, University of New York, "If it does turn out that for some people, there is a genetic or hormonal component (for homosexual behaviour), the cry will then arise to take care of that." Indeed, Louis P Sheldon, president of the Traditional Values Coalition in Anaheim, California, has already remarked that "We have to come up with some reparative therapy to correct that genetic defect."
The evidence that genes play a role in homosexuality in humans came to the fore in the early '90s. A remarkable but controversial find was that there is a difference between the brains of gay and straight men. And in 1993, a researcher from NIH reported that a segment of DNA, containing I or more genes on the X-chromosome, affects sexual orientation. But hard-core evidence linking genes to gayness is yet to be found.