The median frequency of MHMR, ± 95% CI, was determined for wild type, pol4Δ and pol32Δ single mutants, and pol4Δ pol32Δ double mutant cells. A minimum of 15 independent cultures were examined which possess the his3Δ3’ and his3Δ5’ mutant alleles sharing complete (20 bp) or incomplete (14-2-2 bp, 14-2-4 bp, or 14-2-9 bp) microhomologies located on the same chromosome.