(A) Rates of spontaneous unequal SCR, assessed as in Figure 4D. Statistical deviation from wild-type was calculated using a Student’s t-test, **p<0.01. (B) Changes in CAG repeat length were assessed as in Figure 1C. Statistical deviation from wild-type was calculated by Fisher’s Exact Test: *p<0.05, ***p<0.001. (C) Assay to measure BIR at an HO-induced DSB. The first 400 bp of the URA3 gene (UR; right arm) is upstream of an HO cut site (stripes). Homology driven repair of the HO induced DSB can occur with the remaining 404 bp of the URA3 gene (A3; left arm) and if completed via BIR renders the cell URA+ and NATS (Anand et al., 2014). (D) Frequencies of BIR during repair of an HO-induced DSB; SEM of 4–9 replicates is shown (Supplementary file 7). Statistical deviation from wildtype was calculated using a Student’s t-test, ***p<0.001. (E) The type of repair induced by the HO DSB was evaluated by individually scoring all colonies for growth on YC-URA and YEPD+Nat. Colonies that were URA+ NATS are were repaired via BIR. Other types of possible repair events include gene conversion (URA+ NATR), non-homologous end-joining (URA- NATR), and de novo telomere addition (URA- NATS). Statistical analysis of BIR frequencies and repair types can be found in Supplementary file 7.