Since the early days of Konopka and Benzer (1971), who found the first clock gene, fruit flies have been heavily used to understand genetic dissections of behaviors. Genetic dissection is the use of mutation and recombination to piece together the various components of a given biological function.
Animal behavior was once believed to be controlled by a great many genes due to the complex nature of behaviors. The two men mentioned beforehand broke this belief when they demonstrated that a single mutation in a gene could alter the behavior of the flies. Since that time a great many other genes have been mapped, and found to also change the behavior of the flies.
A lot of behaviors are the result of sensory changes. The organs sense the changes and then the mind responses to the change. A major problem that is found while doing this is the ability to repeat the process. This means that depending on what was changed, a special device would have to be made to detect the changes. This device would have to be able to tell the differences between normal and abnormal. In the case of flies, olfactory test are one of the best around.
While the human systems are much more complex the flies, it is important to think about what this means. Maybe humans also have certain genes that control various behaviors that people have. It is much harder to see the correlation between the two, because it would be unethical to do the same tests on people as the flies.