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Fruitless, Behavioral Genetics

by: James Liu

Nearly a century ago, Morgan, Sturtevant, Bridges, and Mullur, pioneers in Drosophila melanogaster (fruit fly) research, used this animal model to elucidate the chromosome model of heredity. They ultimately determined that chromosomes indeed carry genes and are responsible for sex determination. Since then, D. melanogaster has been one of the most widely and thoroughly studied animal models in biology. Much of this is due to the ease in working with D. melanogaster in the lab: its short generation time, lack of genetic recombination in males, and so on. Furthermore, advances in genetic manipulation in generating mutants (P-element insertions and irradiation) has allowed fly researchers to study the function of many genes in Drosophila.

One fascinating field that has gained momentum in fly research is the convergence of behavioral studies and molecular genetics–looking at how genes individually and acting in cohort, influence fly behavior. Determining the link between genetic defect and behavioral alteration is much more complex than merely knocking down a gene and observing the resulting defect. Researchers have studied the relationship between genes and behavior at a holistic perspective, beginning with behavioral defect in these mutations, down to the neurological aberrations, and further down to the molecular changes in these mutations.

Fruitless (fru), for example, is one of these genes. In fruit flies, it is well known as one of the sex determination genes. It was first identified in viable male fru mutants that demonstrated abnormal mating behaviors. Mutant fru males failed to distinguish between male and female mates, whereas mutant fru females are unaffected.1 Various fru mutants that ranges from complete abolition of the gene to merely alteration of the gene have since been created. The “degree” of fru mutation has shown to affect specific steps in males courting behavior. Severe deficiency in fru can abolish male mating behavior entirely. 2 Less severe mutations have resulted in abnormalities in the male’s ability to produce the correct “song” during the mating ritual.3

Fru is also expressed in the central nervous system (CNS) and its expression is the highest when the fly is at its pupal phase. It has been speculated that sensory information transmitted to the CNS is processed by neurophils, the cells that express fru. At a cellular level, fru may be involved in shaping sex-specific neuronal circuitry essential for proper mating behavior.4 However, there remains much to be uncovered in the neurological role of fru in influencing D. melanogaster behavior.

Much is yet to be accomplished in understanding how genes affect behavior. D. melanogaster is an efficient model for this type of study because of the nature of D. melanogaster mating. Mating is divided into specific steps, each requiring a set of visual, tactile, olfactory, and auditory cues. Studying mutants in courting behavior has provided many interesting behavioral abnormalities. But we have yet to make a clear link between how genes coordinate neuronal development and circuitry, which ultimately influences behavior. Many neuronal diseases that we observe today–Alzheimer’s, Parkinson’s, Huntington’s– all have a genetic component of the disease. Thus understanding how genes can affect neurodevelopment and ultimately influence behavior can provide important lessons for understanding how our own genes affect behavior.


1. Solkolwski, M. B., Nature Reviews 2001, 2, 879-890.
2. Goodwin S. F.; Taylor B. J.; Villella A.; Foss M.; Ryner L. C; Baker B. S.; Hall J. C., Genetics, 2000, 154, 725-745.
3. Villella, A.; Gailey, D. A.; Berwald B.; Ohshima S.; Barnes P. T.; Hall J. C., Genetics, 1997, 147, 1107-1130.
4. Baker. B.; Taylor B.; Hall J., Cell, 2001, 105, 13-24.

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