This work will provide a tool for researchers in the C. elegans community. Its goals are to generate overlapping deletions, test existing balancer stocks and create more balancer stocks, and to disseminate the strains. The balancers will be used for maintaining lethal mutations as heterozygotes. The work will be conducted by three co-investigators, Dr. Ann Rose at the University of British Columbia, Dr. David Baillie at Simon Fraser University, and Dr. Donald Riddle at the University of Missouri. Balancers, as originally described in Drosophila, suppress the recovery of recombinant chromosomes. Balances are generally chromosome rearrangements, which may include both inversions, and translocations. At the beginning of the development of this """"""""genetic toolkit"""""""", balancers existed for about one-half of the genome. Currently, chromosome I and III are considered well balanced over the entire chromosome. Chromosomes II, IV, V, and the X are partially balanced. During this grant, the first inversion in C. elegans was reported and its behavior characterized. This inversion has lent support to the hypothesis that the C. elegans chromosomes are monocentric during meiosis. The frequency of finding balancers appears to be region-dependent. The goals of this 3-year project are to use the existing balancers to recover deletions, to map these deletions, to make deletions by targeting them with PCR, and cataloging the strains. This proposal is to continue using four balancers that cover about one-half of the genome. The will be available to the worm community in three versions; these will include those with a recessive visible marker, a dominant visible marker, or a recessive lethal. Deletions will be generated on several chromosomes that contain very few deletions. Treatments such as gamma irradiation, formaldehyde, and ultraviolet irradiation will be used as they have proven successful in other regions of the C. elegans genome. The uncovering of one of two markers that are in repulsion will be used as the primary screen. Two additional screens are proposed. Once strains are produced, the deletion endpoints will be determined using complementation of existing markers in the region. In addition, PCR using previously mapped and sequenced cDNAs will be used to find potential endpoints. Regions that may contain dosage-sensitive loci (haplo- insufficient regions) will be identified. Anew addition to this proposal is the use of deletion tagging and its detection using PCR. This will be used in regions that are under- represented from the classical mutagenesis techniques.