Abstract
The use of a behavioral character, the geotactic response of Drosophila melanogaster, permitted selection in large replicated populations. Each population was derived from the same base population but after the initial selection, it was maintained independently and treated identically. Diallel cross analysis revealed differences between the additive genetic variances of the strains treated in this way. These differences were largest after about eight generations of selection and decreased by the 16th generation.The analysis of diallel tables also showed that the geotactic response in D. melanogaster was controlled by polygenic factors. On the average, the genes that increase the expression of positive geotaxis were partially dominant while factors for negative geotaxis were recessive. Dominance was not, however, always unidirectional.