AskDefine | Define oocyte

Dictionary Definition

oocyte n : a female gametocyte that develops into an ovum after two meiotic divisions

User Contributed Dictionary



  1. A cell that develops into an egg or ovum, a female gametocyte.

Extensive Definition

An oocyte, ovocyte, or rarely oöcyte, is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is part of the ovary development. The germ cells produce a primordial germ cell (PGC) which becomes an oogonia which marks the start of mitosis. After mitosis stops (due to actions of retinoic acid and the mesenephros) meiosis starts. This stage the oogonia is now an Oocyte (pronounced oh'a (like Noah)-site).


The formation of an oocyte is called oocytogenesis, which is a part of oogenesis. Oogenesis results in the formation of both primary oocytes before birth, and of secondary oocytes after it as part of ovulation.



Oocytes are rich in cytoplasm which contains yolk granules to nourish the cell early in development.


During the primary oocyte stage of oogenesis, the nucleus is called a germinal vesicle
The only normal human type of secondary oocyte has sex chromosomes 23,X (where sperm can be 23,X or 23,Y).


The space wherein an ovum or immature ovum is located is the cell-nest.


  • nondisjunction -- a failure of proper homolog separation in meiosis I, or sister chromatid separation in meiosis II can lead to aneuploidy, in which the oocyte has the wrong number of chromosomes, for example 22,X or 24,X. This is the cause of conditions like Down syndrome and Edwards syndrome. It is more likely with advanced maternal age.
  • Some oocytes have multiple nuclei, although it is thought they never mature.



William K. Purves, Gordon H. Orians, David Sadava, H. Craig Heller, Craig Heller (2003). Life: The Science of Biology(7th ed.), pp. 823–824

External links

oocyte in German: Oozyte
oocyte in Spanish: Oocito
oocyte in French: Ovocyte
oocyte in Italian: Ovocita
oocyte in Japanese: 卵母細胞
oocyte in Polish: Oocyt
oocyte in Russian: Ооцит
oocyte in Chinese: 卵母細胞
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