Fig. 1

Proposed mechanisms involved in the formation of structural variation. a DSBs can be repaired by HR, NAHR, NHEJ, MMEJ, and SSA. b FoSTeS and MMBIR model. During DNA replication, the DNA replication fork can stall, leaving the lagging strand to invade another replication fork using complementary template microhomology to anneal and extend by DNA synthesis. The failure to repair by BIR can induce MMBIR, which drives the strand invasion of non-sister templates using microhomology-containing regions, thereby giving rise to chromosomal rearrangements. c LINE-1 or L1-mediated retrotransposition. L1 retrotransposition can mediate the first-strand nick by the endonuclease, followed by first-strand cDNA synthesis with L1 mRNA as the template by reverse transcriptase. The cDNA negative-strand can invade a second 3′ overhang from a preexisting DSB and mediate the synthesis of the second-strand cDNA