Sister chromatids are the two identical copies of the same chromosome attached by the structure called the centromere. These sister chromatids are formed during DNA replication. During the cell division, sister chromatids separate from each other, and each daughter cell receives one copy of chromosomes.
- Sister chromatids consist of two individual chromatids, and these chromatids are half of the replicated chromosomes.
- During the cellular division of both mitosis and meiosis, chromatids are formed.
- Once the sister chromatids are separated during the Anaphase of mitosis, then each separated chromatid is known as a daughter chromosome.
- During the cellular division of meiosis and mitosis, chromatin fibers condense and form chromatids.
- DNA and the skeletal proteins or histone proteins wrap around each other, and the combination is known as a nucleosome. These condensed form of the nucleosome is called chromatids.
- When the nucleosomes are condensed even more tightly, then it is called the chromatin fibers. They condense well enough to fit into the nucleus of a cell.
- After this, chromatin fibers condense themselves even more tightly to form chromosomes.
- A chromosome appears as single-stranded chromatids before DNA replication, but after DNA replication chromosome appears in an X-shape. This X-shaped chromosome is known as sister chromatids.
- The formed sister chromatids separate during the cell division, where each cell acquires a single chromosome.
Sister chromatids in mitosis
- In the Prophase of mitosis: movement of the sister chromatids towards the center of the cell.
- In Metaphase: alignment of the sister chromatids along the metaphase plate at right angles to the cell pole.
- In Anaphase: separation of the sister chromatids and movement towards the opposite pole of the cell. After the separation of the sister chromatids, each chromatid is called a single-stranded full chromosome.
- In telophase and cytokinesis: the sister chromatids that are separated divide into separate daughter cells. The separated chromatids are known as daughter chromosomes.
Sister chromatids in meiosis
Meiosis is similar to that mitosis and is a two-part cell division process.
- In Prophase I and Metaphase I: movement of the sister chromatids in both the phages.
- In Anaphase: homologous chromosomes move to the opposite pole, and sister chromatids remain attached.
- The separation of the sister chromatids does not occur until anaphase II.
- Four daughter cells are produced during the meiosis cell division; each cell receives one-half the number of chromosomes as the original cell.
- Sex cells are also produced by meiosis.
Functions of sister chromatids
- During cell division, the primary function of the sister chromatids is to pass on a complete set of chromosomes to the respective daughter cells.
- Sister chromatids play an essential role in maintaining the integrity of the genome and in DNA repair.
- After the occurrence of chromosomal duplication, this form acts as proofreading in the G2 phase.
- It helps to repair the DNA breaks.
Exchange of sister chromatids
During cell division, the exchange of genetic materials occurs when the two sister chromatids come in close proximity to one another. This process is also known as a sister-chromatid exchange, and a portion of the DNA is swapped during this process. The lower level of exchange is considered safe, while excessive is considered hazardous.