9512811 Lyttle The Segregation distorter (SD) system of meiotic drive in Drosophila melanogaster is important for several reasons: 1) It is involved in the regulation of an important developmental process which is relevant to many eukaryotic organisms, 2) It involves the interaction of regulation of chromatin structure in products from genetic elements in both euchromatin and B-heterochromatin and thus can be considered a model for such interactions, 3) Knowledge of the physical and genetic map of the responder region (Rsp) can provide information on the centromere and adjacent DNA sites regulating position effect variegation and 4) because the SD system exists in a stable polymorphic equilibrium, it offers an excellent model for the evolution of meiosis and spermatogenesis. Two groups of experiments designed to answer questions about the structure and function of the SD system in Drosophila will be done. The first will focus on DNA mapping and cloning of the Rsp region of the 2R heterochromatin. The map will be used to define both genetic deletions and heterochromatic DNA clones which will be introduced. The constructs will be used to quantitate the dependence of SD-mediated sperm dysfunction on Rsp structure. The second is designed to introduce DNA "tags which will allow E(SD) to be cloned. %%% Cytogenetic, molecular and population genetic information will be integrated to provide a dynamic picture of the SD system, its effect on the evolution of gametogenesis and chromosome structure, and its potential as a tool for artificially controlling sex ratio in biocontrol schemes as a long term goal. The more immediate goal is to characterize the DNA structure and function of the second chromosome heterochromatin of Drosophila melanogaster in as much detail as possible. **(
