While many scientists believe that genes contribute to behavior, new research goes several steps further and shows that a single gene directs something as complex as sexual behavior in male fruit flies.
A team of researchers from Stanford and three other universities announced Dec. 12 they had found a gene that controls sexual orientation, courtship and mating in the male insects.
"There has been speculation recently that no single gene could control a complex behavior. This work shows that a gene can do so--at least in fruit flies," said Stanford molecular geneticist Bruce Baker, one of the team's principal investigators.
This is the first discovery of a single gene commanding a complex behavior in an adult animal. "The idea of a single gene is still surprising, that it could control such an elaborate sequence of events," said Lisa Ryner, a Stanford research associate and lead author of the paper published in the peer-reviewed journal Cell last Friday.
The finding is sure to add fuel to the debate about how much genes influence human behaviors.
"The analogy we use is the gene is like a computer running a machine, your body," Ryner said. "The computer depends on inputs, so the outputs can vary. Social and environmental inputs are going to have a big influence. (The gene or computer) is not determining, but it's controlling."
"It's clear--and the authors wrote this in their paper--that human behaviors are much more learned and acquired," said Cori Bargmann, an associate professor at UC San Francisco who studies genetic influences on behavior.
In animals, sexual behavior is more innate. "This is the thing that's really important for an animal to get right. These are the behaviors that are most likely to have a strong biological drive in them," Bargmann said.
The gene is called "fruitless" because it was first found--in mutated form--in males that courted both males and females but never mated. But when the gene operates without any mutations, it acts as a "boss" gene, giving instructions to "employee" genes who work to produce the various aspects of sexual behavior. Flies with severe mutations in the fruitless gene don't court at all, Ryner said.
Researchers found the gene in females fruit flies too, but because their sexual behavior is less obvious, researchers haven't studied the gene's effect on females yet.
Fruitless is part of a network of sex-related genes. A master gene regulates two genes that turn on both fruitless and another gene called doublesex that controls sexual differentiation--whether a fly develops into a male or female.
Like in fruit flies, there is one gene that determines whether humans become male or female. Although fruit flies have only eight chromosomes compared to the 46 in people, the insects are a well-studied, often telling model for human genetics.
"Given this finding . . . it wouldn't be that surprising that a single gene might be able to control something that complex (in humans)," Ryner said.
The gene operates only in a small number of cells in the central nervous system. "Being able to take it from the gene to the brain to behavior is going to be really powerful I think for the scientific community," Ryner said.
The research was a close, four-year collaboration between Stanford, the University of Texas Southwestern Medical Center at Dallas, Brandeis University and Oregon State University.
--Heather Rock Woods
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