Break-induced marker excision concept. Break-induced marker excision concept. A selection marker is flanked by directly repeated sequences (blue arrows) in the genomic region designated “A B C D E F” (top line). A double-strand break within the marker (second line) results in a recombination event between the repeats (third line) that, when resolved, deletes the marker (fourth line). This type of excision reaction was shown to occur in vivo in S. cerevisiae by Sugawara and Haber (11). Mechanistically, the recombination event may occur through the single-strand annealing pathway, the microhomology-mediated end-joining pathway, or other homology-promoted repair events (21). A textbook-style crossover is depicted for simplicity of visualization. Manning Y. Huang, and Aaron P. Mitchell mSphere 2017; doi:10.1128/mSphere.00050-17