Single inseminated founder females in D. melanogaster derived from the same population have led to genetically discrete strains for three quantitative traits, namely scutellar chaeta number, mating speed and duration of copulation. The base population from which the females were derived can therefore be argued to be polymorphic for these traits. Although polymorphisms for genes (or polygenes) for quantitative traits are expected to be ubiquitous in outbreeding species on theoretical grounds, this has not previously been generally demonstrated.