A team of scientists from four universities has isolated the gene that controls most or all sexual behavior in male fruit flies. Their research is the first to pinpoint a single gene that works in the brain to govern nearly all aspects of a complex behavior in adult animals.

The scientists from Stanford, the University of Texas Southwestern Medical Center at Dallas, Brandeis University and Oregon State University report their findings in the Dec. 13 issue of the journal Cell.

The gene fru governs the fly's courtship and mating ritual, including its courting song. Here a male with a normal copy of the gene lifts one wing and vibrates it in a rhythmic song, as recorded on an oscilloscope below the drawing. Males with a slight alteration, or mutation, of the fru gene have subtle changes in their songs. With severe mutations, the flies do not sing a note, though they can flick their wings and can use them to fly. (courtesy: Jeffrey Hall, Brandeis University)

Geneticists have known for years that the gene, called fruitless and nicknamed fru, influences sexual orientation in the fly Drosophila melanogaster. Male flies with some mutations in the fru gene become bisexual -- they cannot tell other males from female flies when courting. With this research, the team of geneticists cloned and isolated the fru gene, and showed that it controls much more than the male's choice of partners.

They showed that the fru gene is:

• A master gene that controls not only sexual orientation but all, or nearly all, the steps in the male fly's elaborate courtship ritual -- from its first interest in a female through its rhythmic courting song, to its attempts to mate.
• Part of a group of genes that work together to govern all aspects of sex in these flies, including development of male and female organs.
• At work in a very small fraction of the cells in the fly's brain. The properties of the
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