Quantitative genetic variation of enzyme activities in natural populations of Drosophila melanogaster

Abstract

The genetic component of variation of enzyme activity in natural populations of D. melanogaster was investigated by using 2 sets of chromosome substitution lines. The constitution of a line of each type is: i1/i1;+2/+2;i3/i3 and i1/i1;i2/i2;+3/+3, where i refers to a chromosome from a highly inbred line and + refers to a chromosome from a natural population. The + but not the i chromosomes vary within a set of lines. By use of a randomized block design to test and estimate components of variance, 50 of the 2nd- and 50 of the 3rd-chromosome substitution lines were screened for variation in the activity levels of 7 enzymes [glucose-6-phosphate dehydrogenase (EC 1.1.1.49), 6-phosphogluconate dehydrogenase (EC 1.1.1.44), fumarate hydratuse (EC 4.2.1.2), .alpha.-glycerophosphate dehydrogenase (EC 1.1.1.8), alcohol dehydrogenase (EC 1.1.1.1), catalase (EC 1.11.1.6) and aldehyde oxidase (EC 1.2.3.1)]. Of the 7 enzymes, 6 show a significant genetic component in at least 1 set of lines, and 5 of the 7 enzymes show activity variations attributable to factors that are not linked to the structural gene. These unlinked activity modifiers identify possible regulatory elements. Analyses of covariance show that most of the genetic variation of enzyme activities cannot be accounted for by genetic variation of live weight or protein content. These results and the lack of strong correlations between the genetic effects on the activities of different enzymes indicate that the effects are mainly specific for individual enzymes.