Mitosis is the process of nuclear division that occurs just prior to cell division or cytokinesis. During mitosis, a cell duplicates all of its contents, including its chromosomes, and splits to form two identical daughter cells. The process of mitosis is carefully controlled by certain genes, and when it is not regulated correctly, health problems such as cancer can result. The key phases of mitosis are:

• Prophase: During this phase, the parent cell chromosomes condense and become thousands of times more compact than they were during interphase. The spindle tubules extend from structures called centrosomes, with one centrosome located at each of the opposite ends, or poles, of a cell. As mitosis progresses, the microtubules attach to the chromosomes, which have already duplicated their DNA and aligned across the center of the cell. The spindle tubules then shorten and move toward the poles of the cell, pulling the one copy of each chromosome with them to opposite poles of the cell.

• Metaphase: During this phase, the chromosomes line up neatly end-to-end along the center (equator) of the cell. The centrioles are now at opposite poles of the cell with the mitotic spindle fibers extending from them. The mitotic spindle fibers attach to each of the sister chromatids.

• Anaphase: During this phase, the sister chromatids are pulled apart by the mitotic spindle, which pulls one chromatid to one pole and the other chromatid to the opposite pole.

• Telophase: During this phase, at each pole of the cell, a full set of chromosomes gather together. A membrane forms around each set of chromosomes to create two new nuclei. The single cell then divides into two identical daughter cells.

Once mitosis is complete, the entire cell divides in two by way of the process called cytokinesis.