Oogenesis

The process of egg formation. The second "o" in oogenesis is pronounced separately from the first: o·o·gen·e·sis. The word was created from the prefix "oo-" (Greek oon, egg) + "genesis" (the coming into being of something) = the coming into being of the egg (the ovum). Oogenesis is in contrast to spermatogenesis, the process of sperm formation.

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Process of formation and development of the ovum. SYN: ovigenesis, ovogenesis. [G. oon, egg, + genesis, origin]

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oo·gen·e·sis .ō-ə-'jen-ə-səs n, pl -e·ses -.sēz formation and maturation of the egg called also ovogenesis

oo·ge·net·ic -jə-'net-ik adj

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n.

the process by which mature ova (egg cells) are produced in the ovary. Primordial germ cells multiply to form oogonium, which start their first meiotic division to become oocyte in the fetus. This division is not completed until each oocyte is ovulated. The second division is only completed on fertilization. Each meiotic division is unequal, so that one large ovum is produced with a much smaller polar body.

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oo·gen·e·sis (o″o-jenґə-sis) [oo- + -genesis] the process of formation of female gametes (oocytes).

Oogenesis, depicting only six of the 46 double-stranded chromosomes (oogonium, primary oocyte), three of the 23 double-stranded chromosomes (secondary oocyte, first polar body), and three of the 23 single-stranded chromosomes (second polar body, spermatozoon, and female and male pronuclei) in human oogenesis, and showing random assortment of homologous chromosome pairs. Crossing over, which may occur in meiosis I, has been omitted. Progression through meiosis II is only completed if fertilization occurs; the spermatozoon and male pronucleus are depicted out of scale for clarity.