Sister chromatid exchange

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

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

Mitosis

sister chromatid. Evidence indicates that, due to the special nearby relationship they share, sister chromatids are not only preferred over distant homologous chromatids as substrates for recombinational repair, but have the capacity to repair more DNA damage than do homologs.^[6]

sister chromatid exchange, rather than by inter-homolog exchange. A molecular-level study of recombination during budding yeast meiosis has shown that recombination events initiated by DSBs in regions that lack corresponding sequences in the non-sister homolog are efficiently repaired by inter-sister chromatid recombination.^[7] This recombination occurs with the same timing as inter-homolog recombination, but with reduced (2- to 3-fold) yields of Holliday junction joint molecules. This study, and comparable evidence from other organisms (e.g. Peacock^[8]), indicates that inter-sister recombination occurs frequently during meiosis, and up to one-third of all recombination events occur between sister chromatids, although mainly by a pathway that does not involve Holliday junction intermediates.^[7]

During oogenesis in the nematode Caenorhabditis elegans the sister chromatid, or even the same DNA molecule, can serve as a meiotic repair template for both crossover and non-crossover recombination.^[9] Non-crossover events are the most frequent recombination outcome. For DNA double strand breaks induced throughout meiotic prophase I, the sister or intra-chromatid substrate is available as a recombinational repair partner.^[9]

See also

• Meiosis
• Homologous recombination
• Sister chromatid

References