Oogenesis
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Oogenesis refers to the process of formation, development, and maturation of a healthy oocyte (egg) in the ovary. In mammals, oogonial transformation into oocytes is completed either before or shortly after birth. The further development comes to a rest during prophase I of meiosis until puberty. In Ascaris, the oocyte does not even begin meiosis until the sperm touches it.
In meiosis, the oocyte divides in four, of which only one becomes an ovum, the others becoming polar bodies. There may be two polar bodies, in which case one is diploid and did not undergo meiosis II.
See also: spermatogenesis