Molecular Population Genetics of a Phosphoglucose Isomerase Polymorphism: Testing Hypotheses of Balancing Selection and Trans-specific Polymorphism

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HARRISON 9318472 National Populations (including human populations) often contain large amounts variation at genes coding for soluble enzymes. The functional significance of this enzyme variation remains a matter of considerable debate. Do enzyme variants in natural populations differ in their functional properties? If so, what forces maintain variation within populations. This project focuses on using DNA sequencing of different allelic forms of the enzyme phosphoglucose isomerase (PGI) to determine what is acting to maintain enzyme variation within species of insects. PGI occupies a central position in carbohydrate metabolism. Catalyzing the interconversion of glucose-6-phosphate and fructose-6-phosphate. The first goal of this research is to characterize the structure of the Pgi gene in two species of crickets, which are both variable for PGI and which have the "same" array of allelic variants (allozymes). Representatives of each of the allelic variants in the two species will then be sequenced. Of particular interest is whether some or all of the amino acid differences that distinguish the allozyme classes are identical in the two species and whether observed amino acid differences are likely maintained in populations by balancing selection. The results will shed light on the general question of the significance of genetic variation for soluble enzymes. Resolution of this issue has implications for understanding the significance of genetic variation in human populations and for questions related to long-term conservation of genetic resources.