Mitosis

Mitosis consists of the following phases:

1. Prophase. The chromosomes begin to condense. Each chromosome was duplicated during the preceding S-phase and so now consists of 2 chromatids. Each of them contains a particular DNA sequence, the centromere, which is necessary for regular separation. The nuclear membrane is still intact. The pairs of centrioles were already duplicated in the G2-phase. The centrosomes with the pairs of centrioles begin to separate out from one another. They synthesize microtubules to create the mitotic spindle.
2. Prometaphase. The chromosomes become fully visible through increasing condensation. The nuclear membrane dissolves. The centrosomes reach the opposite poles of the cell and, along with the microtubules, form the mitotic spindle. One group of microtubules (kinetochore microtubules) anchors to the kinetochore of the chromosomes and agitates them by exerting a force on them. The other group of microtubules meets the ends of the microtubules sprouting from the opposite centrosome (polar microtubules).
3. Metaphase. The kinetochore microtubules line up the chromosomes along the equatorial plane, between the two spindle poles. Each chromosome is held under tension in this metaphase plate by the pairs of kinetochores and their associated microtubules.
4. Anaphase. In each chromosome, the paired kinetochores separate from one other. In this way, every chromatid is slowly pulled to the spindle pole to which it is assigned. The polar microtubules elongate at the same time, which causes the spindles to move further away from each other.