Sister chromatid exchange

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Metaphase spread of a cell line showing a ring chromosome (R) and several sister chromatid exchanges (SCEs), some of which are indicated by arrows.

Sister chromatid exchange (SCE) is the exchange of genetic material between two identical sister chromatids.

It was first discovered by using the Giemsa staining method on one chromatid belonging to the sister chromatid complex before anaphase in mitosis. The staining revealed that few segments were passed to the sister chromatid which were not dyed. The Giemsa staining was able to stain due to the presence of bromodeoxyuridine analogous base which was introduced to the desired chromatid.

The reason for the (SCE) is not known but it is required and used as a mutagenic testing of many products. Four to five sister chromatid exchange per chromosome pair, per mitosis is in the normal distribution, 14-100 exchanges is not normal and presents a danger to the organism. SCE is elevated in pathologies including Bloom syndrome, having recombination rates ~10-100 times above normal, depending on cell type.[1][2] Frequent SCEs may also be related to formation of tumors.

Sister chromatid exchange has also been observed more frequently in B51(+) Behçet's disease.[3]

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  1. ^ "Evidence for increased in vivo mutation and somatic recombination in Bloom's syndrome.". Proc Natl Acad Sci U S A 86 (2): 670–4. Jan 1989. doi:10.1073/pnas.86.2.670. PMC 286535. PMID 2911598. 
  2. ^ "Increased rate of spontaneous mitotic recombination in T lymphocytes from a Bloom's syndrome patient using a flow-cytometric assay at HLA-A locus.". Jpn J Cancer Res 85 (6): 610–8. Jun 1994. doi:10.1111/j.1349-7006.1994.tb02403.x. PMID 8063614. 
  3. ^ Ikbal M, Atasoy M, Pirim I, Aliagaoglu C, Karatay S, Erdem T (February 2006). "The alteration of sister chromatid exchange frequencies in Behçet's disease with and without HLA-B51". J Eur Acad Dermatol Venereol 20 (2): 149–52. doi:10.1111/j.1468-3083.2006.01386.x. PMID 16441621.