Mitosis is the process by which all cells divide. Many cells have a limited life span, and mitosis allows them to be renewed on a regular basis. Mitosis is also responsible for generating the many millions of cells that are needed for an embryo to develop into a fetus, an infant, and finally an adult.

Most human cells continually undergo a cycle of different phases. The phases have distinct names but flow smoothly into one another. The mitotic (M) phase is the phase in which the cell's genetic material is split in two. Once the phase is completed, the cell is physically divided into two daughter cells, in a process called cytokinesis.

Before entering the M phase, cells are in interphase, the phase between two cell divisions. Interphase is itself divided into three phases: G₁, S, and G₂, where G stands for gap or growth, and S for...