In oogenesis, or the female form of gametogenesis, mature egg cells are produced that may be later fertilized. Mammals, including humans, undergo mitosis to form the diploid primary oocyte. The oocyte divides into a haploid secondary oocyte and a polar body by meiosis I. The polar body contains genetic material discarded by the cell and degrades. The secondary oocyte undergoes meiosis II to form a haploid ovum that matures into an egg cell and a second polar body. The second polar body degrades. Each germ cell produces only one mature egg cell. This process is similar in humans and mammals, but varies across all other species.