An ortholog of DNA ligase 3, commonly thought to exist only in vertebrates, also exists in flies. I am using in vivo RNAi and transgenesis to characterize phenotypes of flies lacking this vital protein. Interestingly, certain strains of Drosophila seem to possess at least partial duplications of ligase 3, while others possess the gene only in single copy. My ultimate goal is to use site-specific break repair assays to determine whether or not ligase 3 is involved in alternative end joining in flies.