By the time mitosis proper begins, all the components needed to make two viable daughter cells are present within the parent cell. The four stages of mitosis organize and redistribute those components in preparation for the even physical splitting of one cell into two identical cells.

Prophase
Prophase is the beginning stage of mitosis. The first noticeable change occurs in the chromatin, which gradually coils up and condenses into chromosomes that are visible with a light microscope. At this stage, each chromosome is composed of two identical strands of DNA. The paired strands are called sister chromatids, which are attached to one another at a region known as the centromere.

At the same time the chromosomes are condensing, the two centrosomes (and in animal cells, their centrioles) begin to move to opposite poles of the cell. Microtubules organized by the centrosomes assemble into long spindle fibers that reach across the growing gap between them and help push them apart.

The nuclear membrane gradually disintegrates and the nucleolus disappears, which allows the chromosomes to move freely within the cell. Spindle fibers from each centrosome start to move toward the centromeres.

Prometaphase and Metaphase
During early metaphase (sometimes distinguished as a separate stage called prometaphase) the chromosomes attach to spindle fibers—microtubules from one side of the cell connect to one sister chromatid, and microtubules from the opposite side connect to the other sister chromatid. The tug from opposing fibers begins to pull the chromosomes toward the center of the cell.

Later in metaphase, the centrosomes reach opposite sides of the cell. All of the chromosomes become aligned along a plane at the middle of the cell called the metaphase plate. Each sister chromatid is attached to a spindle fiber leading back to the pole on its side of the metaphase plate. Each chromosome moves and lines up independently of the other chromosomes.

Anaphase
Anaphase is the third stage of mitosis. Proteins holding the sister chromatids together at the centromere split, breaking each duplicated chromosome into two identical strands of DNA. Once they separate, the sister chromatids are called daughter chromosomes.

After the chromosomes split, motor proteins on the centromeres reel them down the attached spindle fibers, and the fibers themselves start to shorten. Both these actions pull the daughter chromosomes away from one another and towards opposite poles of the cell.

Later in anaphase, overlapping spindle fibers, which aren’t attached to chromosomes, lengthen. Motor proteins push the fibers past one another, stretching the spindle and elongating the cell to twice or more it’s original size.

At the end of anaphase an identical group of chromosomes clusters at each pole, and the cell has flattened and stretched, driving the poles as far apart as possible.

Telophase
The last stage of mitosis is called telophase. Microtubules of the spindle apparatus break down in the cytosol. A nucleus reappears as a nuclear envelope forms around each set of chromosomes. The chromosomes decondense and disperse, and fade from view.

Cytokinesis then divides the cell along its midline. In animal cells, a contractile ring of microtubules pinches the cell membrane inwards forming a cleavage furrow, which deepens until it cuts the cell completely across. In plant cells, a cell plate and then a cell wall form across the middle of the cell.

Once cytokinesis is accomplished, there are two separate but identical cells. The new cells then enter into the G1 phase of interphase. These cells will grow and mature and in time continue on into another cycle of mitosis.