Abstract
"Inducibility" of amylase in Drosophila melanogaster was defined and investigated in a natural population from Japan. Inducibility represents the effects of factors remote from the structural gene that control the amount of enzyme produced. Inducibility of an isogenic line is measured as the ratio of the enzyme's specific activity in two different inducing environments. There was considerable genetic variability with respect to inducibility of amylase in 44 isogenic lines derived from a natural population of D. melanogaster . Net fitness and its components in these isogenic lines were also measured. The results indicated that, although the inducibility of the enzyme was positively correlated with the net fitness (r(g) = 0.63 +/- 0.2), the enzyme activities in the normal medium were not (r(g) = 0.12 +/- 0.37). The analysis of the data shows that the differences in inducing factors are mainly responsible for the differences in the fitness of lines and are the genetic materials for the adaptive evolution of organisms.