Repair-Mediated Duplication by Capture of Proximal Chromosomal DNA Has Shaped Vertebrate Genome Evolution
(A) A DNA molecule suffers a double-strand break. The DSB can result in either blunt ends (left), 5′ overhanging ends (center), or 3′ overhanging ends (left). After the break occurs, exonuclease activity (dotted arrow) creates 3′ overhanging ends at the site of the lesion by removing nucleotides from blunt breaks (left) or breaks with 5′ overhanging ends (center). (B) After the exonuclease activity ceases, the resulting breakpoint has 3′ overhangs at both ends of the lesion. (C) In the SDSA pathway, one 3′ overhanging end can invade another DNA molecule, annealing to a sequence that is complementary, and repair synthesis begins. The other 3′ overhanging end may invade a different DNA molecule and begin repair synthesis as well. (D) After repair synthesis is completed and the new strand has dissociated from the template strand, it anneals with the other end of the initial lesion at a complementary region, creating the duplication of one template sequence (left). If both 3′ ends of the lesion used different template strands for repair synthesis, both strands will anneal at a complementary region, resulting in the duplication of two different template sequences (right).