New Drosophila mutant: A new Drosophila mutant, satori, was isolated, the males of which do not court or copulate with female flies.The mutations were identified in the fruitless gene which is responsible for bisexual and homosexual behavior in the satori mutant. It was demonstrated that this mutation in the fruitless gene causes a brain sexual transformation with a concomitant change in sexual orientation.
In the case of the spinster gene, of which mutation in female Drosophila results in extraordinarily strong rejection against courting males, mouse and human homologues were cloned. These genes were mapped on the chromosome, and were used to create a gene knock-out mouse for examining its effect on behavior in mammals.
Evolutionary implications of sexual dimorphism in Drosophila: For the first time sexual dimorphism was found in the brains of several species of Hawaiian Drosophila., in which the male possesses a significant enlargement of one of the glomeruli of the antennal lobe, the olfaction center in the brain. The most conspicuous sexual dimorphism was found in the adiastola species group. The origin of this group is the species ornata in the oldest island, Kauai, which does not exhibit sexual dimorphism of the glomerulus. The moderate sexual difference is found in descendent species cilifera and adaistola, each from the Molokai and Maui islands.The most extreme sexual dimorphism is observed in setosimentum, the youngest species established in the newest island, Hawaii. Therefore, it is likely that the brain sexual dimorphism occurred for the first time in the Maui/Molokai island complex that raised 10-20 million years ago, then further exaggerated in the divergent species through evolution. It is thus possible to demonstrate diverging mating behavior and it's related physiological anatomy during evolution of the Hawaiian Drosophila.