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. 2020 Jan 10;11(1):79. doi: 10.3390/genes11010079

Figure 1.

Figure 1

Cellular pathways of mitotic DNA double strand break repair. In a diploid cell, a DSB may occur in one of the two homologous chromosomes (1). The DSB may be repaired by non-homologous end joining (NHEJ) (2). When repair occurs by homologous recombination (HR), the DSB is first resected (3) to expose areas of single stranded DNA. If direct repeats (green areas) exist on the same chromosome, the break may be repaired by single strand annealing (SSA) (4). If homology is not found, the chromosome may be entirely lost (5). When homology is found elsewhere, the broken ends may invade this region (6). In synthesis dependent strand annealing (SDSA) (7) the invading strand may copy a small region then release and re-anneal. In break induced replication (BIR) (8) the invading strand may copy to the end of the red chromosome. In this case the right part of the broken black chromosome is lost. Occasionally, a more complex double Holiday junction (dHJ) may be established (9), the resolution of which can result in crossovers (CO) or non-crossovers (NCO).