Schwesterchromatids

Schwesterchromatids, or sister chromatids in English, are the two identical copies of a chromosome that arise during DNA replication. They are produced during the S phase and remain physically attached at the centromere by cohesin protein complexes. The centromeric region forms the kinetochore, which mediates attachment to spindle microtubules during cell division.

During mitosis, sister chromatids are aligned at the metaphase plate and then separated into two daughter chromosomes at anaphase, when cohesin is cleaved by separase following the degradation of securin. This separation ensures that each daughter cell receives an identical set of genetic material. In meiosis, sister chromatids remain together through meiosis I; homologous chromosomes segregate in meiosis I while centromeric cohesin is protected by shugoshin. In meiosis II, the sister chromatids finally separate, creating four haploid gametes.

Genetically, sister chromatids are identical; however, replication errors and recombination between homologs during meiosis I can create genetic variation. Recombination between sister chromatids (sister chromatid exchange) can occur at low frequency as a DNA repair pathway but is less common than homologous recombination between homologs.

Schwesterchromatids play a central role in accurate chromosome segregation and genomic stability. Their proper cohesion and timely separation are essential to prevent aneuploidy and related diseases.