Oocyte 559288 219634649 2008-06-16T04:42:19Z PlankBot 7310603 Robot-assisted disambiguation: Egg - Changed link(s) to [[ovum]] {{Infobox Anatomy | Name = Oocyte | Latin = | GraySubject = 3 | GrayPage = 38 | Image = Gray5.svg | Caption = Diagram showing the reduction in number of the [[chromosomes]] in the process of maturation of the [[ovum]]. | Image2 = | Caption2 = | System = | 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&ndash;824 ==See also== * [[Folliculogenesis]] * [[polar body]] ==External links== * [http://it.stlawu.edu/~mtem/devbiol/atlas/ANTRAL1.JPG Slide] {{start box}} {{succession box|title=[[Stages of human development]] |before=None|after=[[Zygote]]|years=Oocyte}} {{end box}} [[Category:Germ cells]] [[de:Oozyte]] [[es:Oocito]] [[fr:Ovocyte]] [[it:Ovocita]] [[ja:卵母細胞]] [[pl:Oocyt]] [[ru:Ооцит]] [[zh:卵母細胞]]