Question

Are sister chromatids formed at the completion of the S phase?

Answer 1

S Phase

1. It is a part of the interphase in the cell cycle where the DNA undergoes replication in the nucleus to create sister chromatids.
2. This occurs between the G1 and G2 phases.
3. Before the S phase, the cell is diploid by having only two sets of chromosomes (2n).
4. The total genetic content of the cell is doubled by the end of the S phase by having 4 sets of chromosomes (4n).

Sister chromatids

1. After the completion of the S phase, a complete set of sister chromatids is formed.
2. The two sister chromatids are attached by kinetochore at the centromeric region.
3. They are visible only when the spindle fibers are attached to the kinetochore and move the sister chromatids to a medial position (metaphase plate).
4. Centrosome which is used to separate the chromatids is also duplicated in the S phase.
5. After the successful duplication and formation of sister chromatids, the cell then proceeds to the G2 phase and then finally to the Mitotic phase.