Evolutionary relationships between gene-structure and gene-regulation variation inDrosophila melanogaster

The evolutionary relationship between gene-structure and gene-regulation variation was examined by using data on allozyme and activity variation for a group of enzyme loci inDrosophila melanogaster. No significant correlation between the two kinds of variation was found, although the present data set is small and probably not sensitive for tests of association. Various hypotheses of association between the two types of variation are discussed and it is shown that any association between gene-structure and gene-regulation variation (positive or negative) would be sensitive to distortion by repeated bottlenecks and genetic drift. Furthermore, random forces would affect gene-structure (allozyme) variation, which is often controlled by one gene, more severely than enzyme activity variation, which is usually controlled by many genes. Measurements of activity variation would appear to provide an evolutionarily more stable and reliable estimate of. loci-specific ‘molecular flexibility’ than measurements of structural variation. It is suggested that locus-specific gene regulation studies employing a set of major alleles would provide a better test of association between gene-structure and gene-regulation variation. The relationship between gene regulation and quantitative variation is discussed and a number of population-genetic questions related to regulatory gene variation are formulated.