TERF1 and infection: Thus, we next classified T-SCEs detected in TRF1 deficient MEFs into these two different types (single and double) and found that 4 days post infection only T-SCEs at single chromatids were significantly increased (Figure 2—figure supplement 2, A-right graph), while the reciprocal exchanges were not enhanced at TRF1 depleted telomeres (Figure 2—figure supplement 2, A-middle graph).