Abstract
Microtubule, chromatin, centrosome, and nuclear envelope configurations during the first division of the Drosophila melanogaster zygote were analyzed in order to investigate the organization of the first cleavage spindle and the origin of the functional centrosome. After pronuclear apposition the parental complements congress at the equatorial plane of the metaphase spindle. The chromatids, however, seem to move to the poles in two separate groups in each half spindle, mingling together during telophase, before the formation of the daughter nuclei. The spatial separation of parental complements during the first mitosis is also supported by the behavior of the nuclear envelope of female and male pronuclei. A low frequency of polyspermy is also observed during fertilization in D. melanogaster.
