A cytological study of a sex-linked, semi-dominant, material effect mutant

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Bannon, Gary A.
Engstrom, Lee E.
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Thesis (M.S.)
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The posterior cytoplasm of the Drosophila melanogaster egg and early embryo is very important because it forms pole cells which are the precursors to the germ cells found in the adult gonads. The posterior portion has been irradiated by many investigators to destroy these pole cells and record the types of effects the deletion has on the developing embryo. A St. Margarita Island strain of D. melanogaster contains a naturally occurring mutation on the X chromosome which affects the development of germ cells in the offspring. This mutation is a semi-dominant, maternal effect, temperature sensitive mutant. In this study female offspring from this strain were examined after having their X chromosomes subjected to 15 generations of selection for expression of agametic gonads. The agametic ovaries of these individuals were examined at the dissecting microscope, light microscope, and electron microscope levels and compared with normal ovaries of Oregon-R wild type females. The mutant ovaries examined contained normal mesodermal components but appeared to lack any developing stem cells or egg chambers. It was concluded that the mutant gene(s) morphological effects occur between the time the pole cells are incorporated into the posterior midgut of the embryo during gastrulation and the time they reach the adult gonad.