Experimental observations of recurrent and non-recurrent genomic rearrangements associated with genomic disorders. The long thin line signifies the genomic region undergoing genomic rearrangements. The black rectangle depicts a gene which is located in the rearranged region and can be affected by the rearrangements. The thick blue (in a) and red (in b and c) bars represent the rearrangements (duplications, deletions or inversions) with their breakpoints a. recurrent rearrangements with a common size and clustered breakpoints. Most of the recurrent rearrangements result from non-allelic homologous recombination (NAHR). The two hatched rectangles flanking the gene depict the low-copy repeats (LCRs) functioning as substrates for NAHR. The rearrangement breakpoints are clustered inside the LCRs. b. Non-recurrent rearrangements. The breakpoints of the non-recurrent rearrangements are scattered in the genomic region. Note, that all of the rearrangements share a common genomic region of overlap, the smallest region of overlap, that encompasses a gene necessary for the conveyed phenotypic trait, which enables these rearrangements to be ascertained. c. Non-recurrent rearrangements with grouping of one breakpoint. Some of the non-recurrent rearrangements have one of their breakpoints localized in one small genomic region. This grouping of breakpoints is distinct from breakpoint clustering, but like clustering, it may reflect underlying genomic architecture (for example, palindrome or cruciform) important to the rearrangement mechanism, depicted as the dotted rectangle in Figure 1c.