Cells divide in two ways—by meiosis or mitosis. Meiosis, coming from the Greek word meaning “less,” occurs in two distinct phases, each phase containing several stages. The activity of the first phase produces two cells. During the second phase, these two cells split again, yielding a total of four cells called gametes. Each gamete contains half the number of chromosomes—called the haploid number—that other cells of the body have. In mammals, these gametes are called eggs when they reside in the female and sperm when they are produced by the male. The other process of cell division is called mitosis, from Greek mitos, “thread of a warp,” and the suffix -osis, “action” or “process.” It occurs in four stages and produces cells that contain a full array—called the diploid number—of chromosomes. These cells, known as somatic cells, are used for the maintenance, functioning, and growth of the body and its parts.
