Synaptonemal complexes during premeiotic DNA synthesis in oocytes of Drosophila melanogaster.

Well-synchronized populations of oocytes obtained by means of the "pupal system" (Grell, 1973a) have been examined to determine the time of appearance of the synaptonemal complex. The complex first appears in the most advanced oocytes between 132 and 138 hr of female development. Between 138 and 156 hr the complex apparently undergoes a fourfold increase in length. At 150 and 156 hr the complex system is extensive and present in virtually all oocytes. Previous studies using the pupal system have placed the period of premeiotic DNA synthesis between 132 and 162 hr. Thus, indirect evidence indicates that a significant portion of synaptonemal complex formation is coextensive with the main DNA replication in the oocyte. Direct evidence that DNA synthesis and complex formation occur simultaneously in oocytes has been obtained by electron microscope autoradiography. By definition, then, the stage of synaptonemal complex formation in Drosophila must include premeiotic interphase.