søsterkromatid

Sister chromatids are two identical copies of a single replicated chromosome that are attached to each other at a region called the centromere. They are formed during the S phase of the cell cycle when DNA replication occurs. Before replication, a chromosome exists as a single DNA molecule. After replication, the chromosome consists of two identical DNA molecules, each forming a sister chromatid. These chromatids are held together by proteins, most notably cohesin.

During cell division, specifically mitosis and meiosis, the sister chromatids separate. In mitosis, sister chromatids are pulled apart to opposite poles of the cell, ensuring that each daughter cell receives a complete set of chromosomes. In meiosis, there are two rounds of division. In meiosis I, homologous chromosomes (which are not sister chromatids) separate. Then, in meiosis II, sister chromatids separate, similar to mitosis, ultimately producing four haploid cells. The precise separation of sister chromatids is crucial for maintaining genetic stability and preventing aneuploidy, which can lead to various genetic disorders.