Fertilization in Drosophila: III. A reevaluation of the role of polyspermy in development of the mutant deep orange

Abstract

Earlier studies on the mutant dor had indicated that, among dor zygotes from mutant mothers, there were two stages of lethality. Mutant daughters died, when the father was also mutant, during meiosis or first cleavages (early lethals); some mutant sons died during these early stages, and others survived to or beyond the blastula stage (late lethals). If the father was wild type there appeared to be an increased frequency of late as opposed to early lethals among the dor Y embryos. It was suggested that the presence of wild-type accessory sperm ( X dor + ) in the cytoplasm of the developing zygote alleviated the adverse influence imposed on the cytoplasm by the dor dor genotype of the mother. Our results indicate that (1) the frequency of polyspermy is not high enough to account for the effect on development that has been proposed; (2) probably many unfertilized eggs were previously misclassified as early lethals, since it was not known until recently that unfertilized eggs complete meiosis; (3) both fertilized and unfertilized eggs from dor females complete meiosis; and (4) fertilized eggs, even when the father is mutant, usually develop to or beyond the early stages of gastrulation, and thus early lethals do not exist typically in the dor stocks. The bearing of precocious meiosis on what appear to be exceptional early lethals is discussed.