Ovarian cytology of an agametic mutant in Drosophila melanogaster
At least some areas of the embryonic blastoderm in Drosophila melanogaster appear to be determined by substances produced under control of the maternal genome without involvement of the embryonic genome. Study of mutant genes controlling the production of such morphogenic substances would provide valuable information about these substances and the nature of determination itself. In this thesis, the adult ovaries in offspring of females containing sex chromosomes originating from a wild-type strain of Drosophila melanogaster collected on Margarita Island, Venezuela have been examined. After selection on such chromosomes, over 50% of the offspring produced by homozygous females contained either one or two agametic gonads. The delayed expression is due to temperature-sensitive gene expression duringoogenesis. Two micron sections of normal and abnormal ovaries of this strain indicate the mesodermal components of the abnormal ovaries including the ovarian sheaths and the ovariole epithelial sheaths, were normal. In addition, attachment of the ovaries to the oviducts are normal. The abnormal ovarioles contain cells which appear to be mesodermally-derived follicle cells, but no normal egg chambers are seen. The germaria also contain follicle cells but no cells resembling stem cells or cystocytes are seen. It is concluded: (1) the development of ovarian germinal and mesodermal components are completely independent and (2) the mutant gene(s) prevent normal differentiation of pole cells into germ cells.