Mitosis is the process by which a nucleate cell divides into two genetically identical daughter cells. These product cells are diploid cells, meaning they have the full 46 chromosomes. There is also no genetic difference at all between the daughter cells, unless there is some abnormality (such as cancer).
Before mitosis even starts, the cell is said to be in interphase, between mitoses. This isn’t really a stage of mitosis because this is the time when a cell performs its usual functions. During interphase, however, something really important happens. The genetic material, right now in a liquid form called chromatin, copies itself. When you think about it, this makes sense, because the daughter cells must have the same genes as the parent cell.
The first stage of mitosis is called prophase. During prophase, the chromatin- the liquid containing strings of DNA- coils up into sausage-like bundles of genetic material known as chromosomes. The identical chromosomes attach at their midpoints, making X shapes called sister chromatids. The nuclear envelope, the membrane around the nucleus, also breaks down during this stage. In addition, twin organelles called centrioles separate and migrate to opposite ends of the cell.
The second phase of mitosis is called metaphase. At the beginning of metaphase, the centrioles begin making a sort of web of cytoskeletal fibers called the mitotic spindle between them. This web will help to push the cell membrane apart. It also serves as a place for the sister chromatids to attach. The mitotic spindle then pulls the attached chromatids to the center of the cell and arranges them in a line.
The third phase of mitosis is anaphase. Now that the mitotic spindle has all the sister chromatids in a line at the center of the cell, it pulls the sister chromatids apart so that each side now has the same genetic material. The spindle pulls the chromosomes to opposite sides of the cell. Meanwhile, the cell membrane begins to squeeze together. This starts to divide the cytoplasm, the liquid inside the cell, in two.
The final phase of mitosis is telophase. Essentially, it is prophase in reverse and doubled. In this phase, the chromosomes on either side of the cell gather together and the mitotic spindle breaks down. A nuclear membrane then forms around both clumps of chromosomes, making two nuclei. The chromosomes then uncoil into chromatin. The cytoplasm finishes squeezing together- a process called cytokinesis- and that’s the end. Now, where there was once only one cell, there are two. It’s taken about 80 minutes from prophase to cytokinesis.
