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 do it.
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 counterparts.
"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 be
Source:North Carolina State University