Cell division is a fundamental biological process that ensures genetic material is accurately distributed to new cells. A parent cell divides to form daughter cells, each receiving a precise copy of genetic information. This accurate distribution is central to maintaining genetic integrity and the proper functioning of living systems.
What Are Sister Chromatids?
Sister chromatids are two identical copies of a single chromosome, joined at a constricted region called the centromere. They form when a cell’s DNA replicates during the synthesis (S) phase of the cell cycle. As long as they are connected, these two identical copies are considered a single chromosome. Sister chromatids ensure each new daughter cell receives a complete and identical set of genetic information.
Separation in Mitosis
Sister chromatids separate during the anaphase stage of mitosis. Mitosis produces two genetically identical daughter cells from a single parent cell. This division supports growth, tissue repair, and the replacement of old or damaged cells.
During metaphase, sister chromatids align along the metaphase plate, with spindle fibers attached to their centromeres. As the cell transitions into anaphase, the cohesin proteins that hold the sister chromatids together are cleaved by an enzyme called separase. This allows the sister chromatids to detach.
Once separated, each chromatid is considered an individual chromosome. Microtubules pull these newly separated chromosomes towards opposite poles of the cell. This movement ensures each forming daughter cell receives a complete set of chromosomes, maintaining genetic consistency.
Separation in Meiosis
In meiosis, sister chromatids separate during Anaphase II, the second meiotic division. Meiosis is a specialized cell division process that produces four genetically diverse haploid cells, such as sperm and egg cells, which are essential for sexual reproduction. This process involves two consecutive rounds of division, Meiosis I and Meiosis II.
During Meiosis I, specifically in Anaphase I, homologous chromosomes separate, but the sister chromatids remain attached to each other. The cells then proceed into Meiosis II, which mechanistically resembles mitosis.
In Metaphase II, the chromosomes, each still consisting of two sister chromatids, align at the metaphase plate. Anaphase II then begins with the simultaneous splitting of the centromeres that held the sister chromatids together. Similar to mitotic anaphase, spindle fibers pull the now-separated sister chromatids (which are again considered individual chromosomes) to opposite poles of the cell. This separation in Anaphase II results in four haploid daughter cells, each containing a single set of unreplicated chromosomes, contributing to the genetic diversity of offspring.