The induction of high tissue levels of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase by dietary sucrose and D-glycerate in Drosophila melanogaster may provide a model system for studying the genetics of the dietary modulation of the pentose phosphate cycle (pentose shunt) in eukaryotes. Strains exhibiting low and high induction responses to sucrose and D-glycerate will be isolated and chromosome interchange methods used to localize the regulatory elements to a particular chromosome. The genetic elements controlling the sucrose and D-glycerate inductions of the pentose shunt enzymes will be mapped by recombination methods and dominance relationships established by standard mating schemes. The relative roles of the oxidative NADP enzymes in lipogenesis will be determined by the biochemical analysis of strains deficient for one or more of the enzymes. The contributions of the pentose shunt enzymes, NADP-malic enzyme and NADP-isocitrate dehydrogenase to the fitness of the individual in different nutritional environments will be assessed by following the gene frequencies of normal and null activity mutant alleles in artificial populations fed fat-free high carbohydrate and fat-free low carbohydrate diets.