A genetic study of the amylase isozyme polymorphism in Drosophila melanogaster

Typescript.Thesis (Ph. D.)--University of Hawaii, 1969.Bibliography: leaves 92-96.viii, 96 l illusMany of the recently discovered genetically determined polymorphisms involving isozymes of Drosophila melanogaster have been concerned with identifying the enzyme biochemically and determining the formal genetics of the enzyme. After the survey of several enzyme systems in natural populations of Drosophila pseudoobscura by Lewontin and Hubby (1966), which indicated that isozyme polymorphisms are more frequent than previously expected, there has been greater interest in population studies of these isozymes as is shown by the recent work in Drosophila melanogaster concerning the Esterase 6 polymorphism (Yarbrough and Kojima, 1967) and the alcohol dehydrogenase polymorphism (Kojima and Tobari, 1969b). The purpose of this study was to investigate the frequencies of the amylase isozyme alleles in several natural populations of D. melanogaster, and on the success of this investigation, to attempt to see how the polymorphism might be maintained. The survey consisted of recently collected flies from natural populations of Texas and Wisconsin. In addition, the Odate population (collected in Japan four years ago and since kept in the laboratory) was also examined. For all surveys the frequency of the Amyl allele was clearly the most common (0.80) and was followed by Amy1,3 (about 0.12). Other less frequent alleles observed were Amy2,3, Amyl,2, and hmy1,6. Because of Amyl and Amy1,3 being consistently the most frequent in the natural populations, the selection studies concentrated on these two alleles in the Texas and Wisconsin populations. The results of the viability and fertility experiments (for matings within and between populations) consistently demonstrated higher viability and fertility for the Amyl,3/Amyl,3 genotype followed by Amyl/Amyl,3 and Amyl/Amyl genotypes respectively. The results of the developmental study, which employed the normal sugar containing media and a special media containing starch instead of sugar, were less consistent; however, the Amyl/Amyl genotype had the slowest developmental time with the Amyl/Amyl,3 and Amyl,3/Amyl,3 genotypes being similar to each other. From these results it is difficult to see why the Amyl has such a high gene frequency in natural populations. There was some indication from one of the viability experiments that the recovery frequency of the Amyl allele among progeny is higher than that of the Amyl,3 allele when the parents are very young, thus suggesting a prezygotic mechanism of some sort. This study, however, does not critically test for prezygotic selection and more specific tests are currently being planned