Tissue specificity of enzyme expression regulated by diffusible factors: evidence in Drosophila hybrids.

Pairs of hybridizable species of Hawaiian picture-winged Drosophila differ qualitatively in the distributions of specific enzymes in their tissues. An examination of the patterns of enzyme expression in the hybrids showed that, in three instances, absence of an enzyme from a specific tissue was dominant to presence. Since other developmental features indicated that both parental genomes were functioning, these results suggest that, in these cases, the pattern differences in the parental species were due to diffusible factors that affected expression of the relevant structural genes rather than to differences in the genes themselves or in cis-acting regulatory sites.