Behavior and cytogenetics of fruitless in Drosophila melanogaster: different courtship defects caused by separate, closely linked lesions.

The fruitless (fru) courtship mutant was dissected into three defects of male reproductive behavior, which were separable as to their genetic etiologies by application of existing and newly induced chromosomal aberrations. fru itself is a small inversion [In(3R) 90C; 91B] on genetic and cytological criteria. Uncovering the fru distal breakpoint with deletions usually led to males with two of the fru courtship abnormalities: no copulation attempts with females (hence, behavioral sterility) and vigorous courtship among males, including the formation of "courtship chains." However, certain genetic changes involving region 91B resulted in males who formed courtship chains but who mated with females. Uncovering the fru proximal breakpoint led to males that passively elicit inappropriately high levels of courtship. This elicitation property was separable genetically from the sterility and chain formation phenotypes and provisionally mapped to the interval 89F-90F, which includes the fru proximal breakpoint. Behavioral sterility and chaining were also observed in males expressing certain abnormal genotypes, independent of the fru inversion. These included combinations of deficiencies, each with a breakpoint in 91B, and a transposon inserted in 91B.