A genetic analysis of homologous genetic recombination in the plant Arabidopsis thaliana will be done. Mutants which are defective in recombination or which have elevated levels of recombination will be isolated. These mutants will be mapped and characterized by genetic analysis. The first immediate goal of this proposal is to identify suitable marker systems for rapid, accurate measurement of meiotic and mitotic recombination so that these methods may be used to identify and characterize mutants. The second goal is to screen an existing set of DNA repair deficient mutants as well as newly mutagenized plants for individuals with abnormal recombination frequencies. The third goal is to characterize the relationship between repair and recombination in Arabidopsis. This work will establish a genetic system that will make a molecular analysis of recombination in plants become feasible.