such as "Introduction", "Conclusion"..etc
September 23, 2006 — Even the tiny, mild-mannered
fruit fly can be a little mean sometimes – especially when there’s a
choice bit of rotten fruit to fight over. And, like people, some flies
have shorter tempers than others.
Researchers in the North Carolina Sate University genetics
department have identified a suite of genes that affect aggression in
the fruit fly Drosophila melanogaster, pointing to new mechanisms that
could contribute to abnormal aggression in humans and other animals.
The study, led by doctoral student Alexis Edwards in the laboratory
of Dr. Trudy Mackay, William Neal Reynolds Professor of Genetics,
appears online in PloS Genetics.
Feisty flies themselves may not be very scary, but their genes and
biochemistry have more in common with those of humans than the casual
observer might suspect, and geneticists can subject flies to
experiments that simply can’t be done on higher organisms.
To measure aggression, the researchers starved male flies for an
hour and a half, then gave them a small food droplet and watched them
duke it out, counting the number of times a focal fly would chase,
kick, box, or flick his wings at other flies.
“Some animals will very vigorously defend their little food patch,
whereas others are relatively polite,” Mackay said. “To determine if
this had a genetic basis, we conducted a selection experiment.”
For the selection experiment, Edwards pulled three groups of flies –
high aggression, low aggression and control – from the same baseline
population, and kept them separate for 28 generations. From each
generation, she selected the most aggressive flies from the high
aggression group, the least aggressive flies from the low aggression
group, and a random sample of the control flies, to be the parents of
the next generation.
All the flies started at the same level of aggression, but after 28
generations of selection, the high aggression groups were kicking,
chasing and boxing more often, while low aggression groups would hardly
fight at all.
Selection experiments only show these kinds of results when there is
some genetic control over the trait being selected. In this case, the
genetic effect was not very strong – the heritability, or genetic
contribution to, aggressive behavior was about 10 percent. The other 90
percent had to be attributed to environmental variation.
“This is definitely not genetic predeterminism,” Mackay said. “It’s
a susceptibility. Even in flies, in the constant environment in which
we grow them, the environment is more important than the genes. But we
are very interested in that small genetic contribution.”
Next, the researchers wanted to know which specific genes affect a
fly’s chances of becoming a bully. To find out, they conducted a
microarray experiment, a way of comparing which genes are turned on or
off, or up or down, in aggressive versus non-aggressive flies.
They found 1,539 genes that were expressed differently in the two
groups – and flies only have about 14,000 genes in all. It will take
more work to find out which of these genes directly affect aggressive
behavior, which ones change as a result of the behavior, and how they
But Edwards started by studying 19 families of flies, each of which
had a single mutation in one of the genes identified in the microarray
experiment. Fifteen of those 19 mutant families did, in fact, display
abnormal aggression compared to non-mutants, confirming the role of
those specific genes in aggressive behavior.
Those genes were already known to affect nervous system development,
metabolism and immunity, among other things – but none of them had been
previously implicated in aggression. Many of them have human
“Now we have 15 completely novel genes we can use in the future to
investigate aggressive behavior,” Mackay said. “Ultimately we hope to
understand the basic biology of this very important trait, because the
better we understand it in flies, the more we can develop logical human
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