[Paleopsych] NYT: For Fruit Flies, Gene Shift Tilts Sex Orientation
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Fri Jun 3 19:38:34 UTC 2005
For Fruit Flies, Gene Shift Tilts Sex Orientation
New York Times, 5.6.3
By ELISABETH ROSENTHAL,
International Herald Tribune
When the genetically altered fruit fly was released into the
observation chamber, it did what these breeders par excellence tend to
do. It pursued a waiting virgin female. It gently tapped the girl with
its leg, played her a song (using wings as instruments) and, only
then, dared to lick her - all part of standard fruit fly seduction.
The observing scientist looked with disbelief at the show, for the
suitor in this case was not a male, but a female that researchers had
artificially endowed with a single male-type gene.
That one gene, the researchers are announcing today in the journal
Cell, is apparently by itself enough to create patterns of sexual
behavior - a kind of master sexual gene that normally exists in two
distinct male and female variants.
In a series of experiments, the researchers found that females given
the male variant of the gene acted exactly like males in courtship,
madly pursuing other females. Males that were artificially given the
female version of the gene became more passive and turned their sexual
attention to other males.
"We have shown that a single gene in the fruit fly is sufficient to
determine all aspects of the flies' sexual orientation and behavior,"
said the paper's lead author, Dr. Barry Dickson, senior scientist at
the Institute of Molecular Biotechnology at the Austrian Academy of
Sciences in Vienna. "It's very surprising.
"What it tells us is that instinctive behaviors can be specified by
genetic programs, just like the morphologic development of an organ or
The results are certain to prove influential in debates about whether
genes or environment determine who we are, how we act and, especially,
our sexual orientation, although it is not clear now if there is a
similar master sexual gene for humans.
Still, experts said they were both awed and shocked by the findings.
"The results are so clean and compelling, the whole field of the
genetic roots of behavior is moved forward tremendously by this work,"
said Dr. Michael Weiss, chairman of the department of biochemistry at
Case Western Reserve University. "Hopefully this will take the
discussion about sexual preferences out of the realm of morality and
put it in the realm of science."
He added: "I never chose to be heterosexual; it just happened. But
humans are complicated. With the flies we can see in a simple and
elegant way how a gene can influence and determine behavior."
The finding supports scientific evidence accumulating over the past
decade that sexual orientation may be innately programmed into the
brains of men and women. Equally intriguing, the researchers say, is
the possibility that a number of behaviors - hitting back when feeling
threatened, fleeing when scared or laughing when amused - may also be
programmed into human brains, a product of genetic heritage.
"This is a first - a superb demonstration that a single gene can serve
as a switch for complex behaviors," said Dr. Gero Miesenboeck, a
professor of cell biology at Yale.
Dr. Dickson, the lead author, said he ran into the laboratory when an
assistant called him on a Sunday night with the results. "This really
makes you think about how much of our behavior, perhaps especially
sexual behaviors, has a strong genetic component," he said.
All the researchers cautioned that any of these wired behaviors set by
master genes will probably be modified by experience. Though male
fruit flies are programmed to pursue females, Dr. Dickson said, those
that are frequently rejected over time become less aggressive in their
When a normal male fruit fly is introduced to a virgin female, they
almost immediately begin foreplay and then copulate for 20 minutes. In
fact, Dr. Dickson and his co-author, Dr. Ebru Demir of the Institute
of Molecular Biotechnology, specifically chose to look for the genetic
basis of fly sexual behavior precisely because it seemed so strong and
instinctive and, therefore, predictable.
Scientists have known for several years that the master sexual gene,
known as fru, was central to mating, coordinating a network of neurons
that were involved in the male fly's courtship ritual. Last year, Dr.
Bruce Baker of Stanford University discovered that the mating circuit
controlled by the gene involved 60 nerve cells and that if any of
these were damaged or destroyed by the scientists, the animal could
not mate properly. Both male and female flies have the same genetic
material as well as the neural circuitry required for the mating
ritual, but different parts of the genes are turned on in the two
sexes. But no one dreamed that simply activating the normally dormant
male portion of the gene in a female fly could cause a genetic female
to display the whole elaborate panoply of male fruit fly foreplay.
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