Oocyte
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Robot-assisted disambiguation: Egg - Changed link(s) to [[ovum]]
{{Infobox Anatomy |
Name = Oocyte |
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Image = Gray5.svg |
Caption = Diagram showing the reduction in number of the [[chromosomes]] in the process of maturation of the [[ovum]]. |
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MeshName = Oocytes |
MeshNumber = A05.360.490.690.680 |
}}
An '''oocyte''', '''ovocyte''', or rarely '''oöcyte''', is a female [[gametocyte]] or [[germ cell]] involved in [[biological reproduction|reproduction]]. In other words, it is an [[immature ovum]], or [[ovum|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'').
==Formation==
{{Main|Oogenesis}}
The formation of an oocyte is called oocytogenesis, which is a part of oogenesis<ref>[http://www.answers.com/topic/oogenesis?cat=health answers.com]</ref>. Oogenesis results in the formation of both '''primary oocytes''' before birth, and of '''secondary''' oocytes after it as part of [[ovulation]].
{| class="wikitable"
| '''Cell type''' || '''[[ploidy]]/[[chromosomes]]''' || '''[[chromatids]]''' || '''Process''' || '''Time of completion'''
|-
| [[Oogonium]] || diploid/46 || 2N || [[Oocytogenesis]] ([[mitosis]]) || third [[trimester]]
|-
| '''primary Oocyte''' || diploid/46 || 4N || [[Ootidogenesis]] ([[meiosis]] 1) ([[Folliculogenesis]]) || [[Dictyate]] in prophase I until ovulation
|-
| '''secondary Oocyte''' || haploid/23 || 2N || [[Ootidogenesis]] ([[meiosis]] 2) || Halted in metaphase II until fertilization
|-
| [[Ootid]] || haploid/23 || 1N || ? || Minutes after fertilization
|-
| [[Ovum]] || haploid/23 || 1N ||
|}
==Characteristics==
===Cytoplasm===
Oocytes are rich in [[cytoplasm]] which contains yolk granules to nourish the cell early in development.
===Nucleus===
During the primary oocyte stage of oogenesis, the nucleus is called a germinal vesicle<ref>[http://www.biology-online.org/dictionary/Germinal_vesicle Biology-online]</ref>
The only normal human type of secondary oocyte has sex chromosomes 23,X (where sperm can be 23,X or 23,Y).
===Nest===
The space wherein an ovum or immature ovum is located is the ''cell-nest''<ref>[http://www3.interscience.wiley.com/cgi-bin/abstract/114123711/ABSTRACT?CRETRY=1&SRETRY=0 Germinal epithelium, folliculogenesis, and postovulatory follicles in ovaries of rainbow trout, Oncorhynchus mykiss (Walbaum, 1792) (Teleostei, protacanthopterygii, salmoniformes)] </ref>.
==Abnormalities==
* [[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 [[cell nucleus|nuclei]], although it is thought they never mature.
==References==
<references/>
== Resources ==
William K. Purves, Gordon H. Orians, David Sadava, H. Craig Heller, Craig Heller (2003). ''Life: The Science of Biology''(7th ed.), pp. 823–824
==See also==
* [[Folliculogenesis]]
* [[polar body]]
==External links==
* [http://it.stlawu.edu/~mtem/devbiol/atlas/ANTRAL1.JPG Slide]
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{{succession box|title=[[Stages of human development]] |before=None|after=[[Zygote]]|years=Oocyte}}
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[[Category:Germ cells]]
[[de:Oozyte]]
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[[it:Ovocita]]
[[ja:卵母細胞]]
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[[ru:Ооцит]]
[[zh:卵母細胞]]