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. 2022 Jun 14;15:23. doi: 10.1186/s13039-022-00600-6

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© The Author(s) 2022

Open AccessThis article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.

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Fig. 7 — 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)