Final answer:
Chromatids separate and migrate towards the poles during anaphase, the third phase of mitosis. In prophase, chromosomes become visible, and spindle fibres attach to kinetochores in prometaphase. Chromosomes align themselves on the metaphase plate during the metaphase stage of the cell cycle.
Step-by-step explanation:
During mitotic division, chromatids separate and migrate towards the poles during anaphase. This is the third phase of mitosis, when sister chromatids are pulled apart by the shortening of the spindle fibers. After separation, they are called chromosomes.
As for when chromosomes become visible under a light microscope, it happens during prophase, which is the first stage of mitosis. In prometaphase, mitotic spindle fibres attach to kinetochores of each sister chromatid. Then, the chromosomes align on the metaphase plate during metaphase. Following these stages, in anaphase, the sister chromatids are finally separated and move to opposite poles of the cell.