Oogonium

Oogonium is a biological term used to denote the diploid germ cell that gives rise to the female gamete in certain organisms. In animals, oogonia are the embryonic or fetal germ cells that reside in the developing ovaries and divide by mitosis to expand the female germ line. At the onset of meiosis, they become primary oocytes and arrest at prophase I. After puberty, a small number of primary oocytes resume meiosis during each ovulatory cycle, producing a secondary oocyte and a first polar body in meiosis I. Meiosis II is completed only if fertilization occurs, yielding the mature ovum and a second polar body. Thus, oogonia are the precursors to eggs rather than the mature egg cells themselves.

In plants, algae, and some fungi, oogonium refers to the female gametangium or the structure that produces the egg cell. In these groups, the egg is formed within a protective gametangial or gametophytic environment, and fertilization leads to a diploid zygote that develops into the next generation. The precise development and cellular origin of oogonia can vary across taxa, but the common role is to generate the female gamete.

The term derives from Latin and Greek roots meaning 'egg' and 'to beget.' Oogonia are a key component in the study of gametogenesis and reproductive biology across diverse life forms.