Mi{DR-white.3xP3-DsRed} is designed to measure the repair of an induced double strand break (DSB) in vivo; it directly measures the frequency of homologous recombination (HR) and also detects nonhomologous end-joining (NHEJ) and single-strand annealing (SSA) events. It contains two non-functional copies of the w gene; 'Sce.white' and 'iwhite', with the two copies separated by a Disc\RFP^{DsRed.3xP3.cUa} marker. 'Sce.white' is non-functional due to the insertion of an 18bp RS(I-SceI) site (plus an additional nucleotide) at the wild-type SacI site, resulting in an in-frame premature stop codon. 'iwhite' is non-functional due to 5' and 3' truncations that remove the promoter, 5' UTR, start codon, the last 30 amino acids, and the 3' UTR. Expression of I-SceI can induce a DSB at the RS(I-SceI) site, and this DSB can be repaired in premeiotic germline cells and mitotically dividing somatic cells. The relative contribution of each of the HR, NHEJ and SSA pathways to the repair can be quantitated by analyzing the phenotype of the progeny (premeiotic male germline repair events) or by PCR and sequence analysis (somatic and germline repair events).