Schwesterchromatid

Schwesterchromatid refers to one of the two identical copies of a chromosome that are produced during DNA replication. The two copies stay joined at the centromere and form a replicated chromosome until they are segregated during cell division. In English, the term is sister chromatid, and the plural is sister chromatids.

Formation and structure: During the S phase of the cell cycle, each chromosome is replicated, producing two sister chromatids that are virtually identical in DNA sequence. They are held together by cohesin protein complexes along the length, with the centromere containing the kinetochore, the structure that attaches to spindle fibers during division.

Separation: In mitosis, during anaphase, separase cleaves cohesin, allowing the chromatids to be pulled to opposite poles by spindle microtubules. In meiosis II, sister chromatids separate to form distinct daughter chromosomes. In meiosis I, homologous chromosomes separate, while sister chromatids remain joined at least until meiosis II. After separation they are considered individual chromosomes.

Terminology and context: The term Schwesterchromatid is common in German-language biology texts; in English, the usual term is sister chromatid (plural sister chromatids). Sister chromatids are genetically identical except for potential rare mutations; recombination between sister chromatids is rare but can occur in processes such as sister chromatid exchange (SCE) assays.