The regulation of sister-chromatid segregation in Drosophila will be analyzed. While disjunction of sister-chromatids is common to both meiosis and mitosis, in meiosis sister-chromatid separation occurs in meiosis II and is inhibited in meiosis I. Thus there are functions that promote sister-chromatid cohesion as well as those that lead to disjunction. Two Drosophila mutants, mei-S332 and ord, result in precocious sister-chromatid separation in meiosis I of both males and females, providing a key to unraveling this process. We have recently isolated additional alleles of each of these loci; these alleles reveal that the mei-S332 is not required to maintain sister-chromatid cohesion until anaphase I, after the kinetochore has duplicated. The new alleles of mei-S332 will be analyzed for their effects on sister-chromatid segregation in meiosis and mitosis using genetic and cytological approaches. The mei-S332 gene will be cloned and its products identified and characterized. Since an interesting possibility is that the gene encodes a component of the kinetochore which functions to maintain cohesion or the two duplicated halves, the cytological location of the mei-S332 gene product will be analyzed. Sister-chromatid disjunction is central to the ordered segregation of chromosomes is eukaryotic organisms. The information resulting from this work will allow us to understand better fundamental aspect of inheritance.
