a | Dicentric chromosomes formed by telomere fusion rarely, if ever, break during mitosis and instead form chromatin bridges. b | Daughter nuclei connected by chromatin bridges undergo frequent nuclear envelope (NE) rupture in interphase (NERDI), resulting in the accumulation of 3′ repair exonuclease 1 (TREX1) on bridge DNA. TREX1-mediated resection of DNA leads to the formation of single-stranded DNA (ssDNA), which is bound by replication protein A (RPA), and bridge resolution. Bridge fragments are internalized into the nucleus where they remain associated with RPA for approximately 24 hours. c | Part of the dicentric chromosome that is present in the chromatin bridge undergoes extensive fragmentation followed by haphazard repair, which yields a chromothriptic chromosome in which many original chromosome fragments are lost and retained fragments are present in seemingly random order and orientation. Chromothriptic breakpoints are frequently associated with kataegis mutation clusters.