Figure 1From: A mitotic recombination map proximal to the APC locus on chromosome 5q and assessment of influences on colorectal cancer risk (a) Examples and (b) probable mechanism of LOH by mitotic recombination involving APC. (a) Illumina Beadstudio B allele frequency (upper) and Log R ratio plots from colorectal adenomas 3469-1-J-2 (breakpoint, 68–70 Mb) and 2079-L-AC-1 (66–69 Mb). CRC cell lines C170 (~79 Mb) and VACO4S (70–75 Mb) are shown for comparison. LOH is indicated by the splitting of the heterozygous calls around the B = 0.5 region. Note the copy number loss in 3469-1-J-2 at the mitotic recombination boundary, suggesting germline copy number variation or deletion of sequences as a result of recombination. (b) A highly simplified version of LOH by mitotic recombination. It is envisaged that a protein-truncating mutation in APC is present on one copy of chromosome 5. The other chromosome 5 then suffers a double strand break on its long arm proximal to APC. Rather than using a sister chromatid for repair (for example, if the break has not occurred during or after S phase), repair is effected (dashed line) using the other copy of chromosome 5 as a template. This causes the distal long arms of the two chromosome 5 s, including the APC mutation, to become genetically identical and hence LOH at APC occurs.Back to article page