Chromatids start moving towards the respective poles in:

Explanation

During anaphase of mitosis, chromatids move towards opposite poles of the cell due to the actions of spindle fibers, also known as microtubules. Anaphase is the stage of mitosis where sister chromatids separate and are pulled apart to opposite ends (poles) of the cell. This process ensures that each daughter cell receives a complete set of chromosomes.The movement of chromatids during anaphase occurs in the following steps:1. **Shortening of Spindle Fibers:** Microtubules that make up the spindle fibers begin to shorten. This shortening is facilitated by motor proteins that walk along the microtubules, pulling the chromosomes towards the poles.2. **Separation of Sister Chromatids:** The protein complexes called kinetochores, located at the centromere of each chromosome, serve as attachment sites for spindle fibers. As the spindle fibers shorten, they exert force on the kinetochores, pulling the sister chromatids apart.3. **Movement towards Poles:** As the spindle fibers pull on the kinetochores, the sister chromatids are dragged towards opposite poles of the cell. This movement ensures that each daughter cell will receive an identical set of chromosomes.4. **Cytokinesis:** Concurrently with anaphase, the cell undergoes cytokinesis, during which the cytoplasm divides, resulting in the formation of two separate daughter cells, each containing a complete set of chromosomes.The movement of chromatids towards the poles during anaphase ensures that each daughter cell receives an identical and complete set of chromosomes, which is crucial for maintaining genetic integrity and ensuring the proper functioning of cells.