Fig. 7
From: Mechanisms of structural chromosomal rearrangement formation
Mechanisms of formation of inverted duplications associated with terminal deletions (inv dup del rearrangements). A U-type Exchange Mechanism: (a) a double-strand break in sister chromatids leads to a terminal deletion. (b) Fusion of the broken ends forms a symmetric U-type structure and produces a dicentric chromosome, which undergoes another double-strand break forming the (c) inv dup del chromosome without the spacer between the duplicated region (shown as blue arrows). B Low Copy Repeat-dependant Mechanism: (a) LCRs in inverted orientation located in sister chromatids lead to (b) a partial folding of a chromatid onto itself so that the LCRs can pair and align with the other chromatid. A crossing over event can happen between them and form (c) a dicentric chromosome, which undergoes a double-strand break and forms the (d) inv dup del chromosome, which presents a spacer flanked by the LCRs between the duplicated region (shown as blue arrows). C Paracentric Inversion-dependant Mechanism: (a) Two homologous chromosomes with one (bottom) presenting an inversion (e′–d′). (b) Formation of an inversion loop to allow for proper chromosome pairing with the normal homolog during meiosis. (c) A crossing over event happens within the loop and leads to the formation of (d) a dicentric chromosome, which undergoes a double-strand break and forms the (d) inv dup del chromosome, which presents a spacer between the duplications (shown as blue arrows). D Fold-back Mechanism: (a) Chromosome with microhomologies (shown in purple). (b) A double-strand break forms the terminal deletion. (c) A 5′ to 3′ resection creates a 3′ overhang with exposed microhomologies. (d) Due to the microhomologies, the 3′ overhang folds back onto itself and allows for intrastrand pairing. (e) DNA synthesis fills the resected gap forming a monocentric fold back chromosome, and (f) DNA replication forms a dicentric chromosome, which suffers a (g) double strand break forming an (h) inv dup del chromosome, which presents a spacer between the duplicated region (shown as blue arrows)