The signals essential to Drosophila melanogaster courtship include pheromones emitted by the female which stimulate the male to court and pheromones emitted by the courting male which stimulate the female to accept. Genetic variation among these phermones is a common (if not universal) requirement for stimulation of either sex. The signal from the courting male to the female involves both a volatile and a nonvolatile component. The volatile component is associated with loci on the second and/or third chromosomes, while the monvolatile component is associated with the X and/or fourth chromosomes. This widespread distribution in the genome of loci controlling various components in the communication network inevitably results in linkage associations with other loci. The genetic array of gametes was limited. When combined with the negative assortitative mating pattern produced by the stimulation by dissimilar pheromones, linkage disequilibrium creates a strong counterforce to inbreeding during population bottlenecks.