Oocyten

Oocytes are the female germ cells, also known as egg cells, that are essential for sexual reproduction in animals and plants. They are produced by the female parent during gametogenesis, a process of cell division that results in mature gametes. In humans, oocytes are formed during oogenesis, which begins before birth and continues through a woman's reproductive years. An immature oocyte is called an oogonium. After undergoing a series of growth and maturation phases, it becomes a primary oocyte, which is arrested in meiosis I. Upon ovulation, the primary oocyte completes meiosis I, forming a secondary oocyte and a polar body. The secondary oocyte then enters meiosis II, but it arrests again at metaphase II, waiting for fertilization. If fertilization occurs, the secondary oocyte completes meiosis II, producing a mature ovum (egg cell) and another polar body. Oocytes are typically large, non-motile cells containing the genetic material from the female parent, as well as vital nutrients and cytoplasmic factors that will support the development of the embryo after fertilization. The number of oocytes a female possesses is finite and decreases with age, contributing to the decline in fertility.