For cells to repair damage and grow tissue, they must replicate themselves. Throughout most of your body, this replication process is called mitosis. During mitosis, a single cell goes through several stages of division to produce two daughter cells that are identical to the original cell. Although each stage of mitosis is critical for the formation of the daughter cells and each can be observed under a microscope, three of the most distinct stages you'll observe are interphase, metaphase and anaphase.
Interphase is the stage of mitosis during which the cell is not actively dividing, but that doesn't mean the cell is at rest. Instead, the cell grows, produces proteins and duplicates its chromosomes in preparation to divide. Because the majority of a cell's life is spent in interphase, you shouldn't have to search too long to find a cell in this stage. Under the microscope, you'll see a cell with a nucleus, but you won't be able to clearly see chromosomes. At the later stage of interphase, you'll see dark spots near the nucleus. During prophase, these dark spots will develop into centrosomes. As the centrosomes move to opposite ends of the cell, they form a spindle of microtubules.
As a cell heads into metaphase, the membrane around the nucleus breaks apart, freeing the chromosome pairs that were housed inside the nucleus. Just prior to metaphase, the fibers from the centrosomes extend from the poles of the cell to the center line of the cell. During metaphase, the chromatids line up along the equator of the cell. Once aligned, one fiber from the north pole of the cell and one fiber from the south pole of the cell attach to each sister of a chromosome pair. Under the microscope, the line of chromosomes across the equator of the cell makes metaphase one of the most recognizable stages of mitosis.
During anaphase, the cell grows larger to prepare to divide. As the cell grows, the poles become further apart, moving the centrosomes with them. This movement of the centrosomes pulls on the fibers that are attached to the chromosomes and eventually pulls each chromosome pair apart. One of the pair will go to the north end of the cell, while the other will go to the south pole. A cell in anaphase will show the chromosome pairs drifting away from one another as they head to the opposite ends of the cell.
Before the cell can return back to interphase, it must complete mitosis. In telophase, the chromosome pairs reach the opposite ends of the cell and the fibers attached to them break apart. As nuclear membranes form around the two sets of chromosomes, the chromosomes become less distinct under the microscope. In cytokinesis -- the final stage of mitosis -- a furrow develops at the center of the cell. This furrow eventually pinches in and divides the cell in two. The cells then return to interphase until it's time to divide again.
