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Oocyte
Diagram showing the reduction in number of the chromosomes in the process of maturation of the ovum.
Latin '
Gray's subject #3 38
System
MeSH A05.360.490.690.680
[[Image:|190px|center|]]

An oocyte, ovocyte, or rarely ocyte, 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 oogonium 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-site).

[[==Formation==

Main article: Oogenesis

The formation of an oocyte is called oocytogenesis, which is a part of oogenesis[1]. Oogenesis results in the formation of both primary oocytes before birth, and of secondary oocytes after it as part of ovulation.

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 ]iiqqhtdres]

CharacteristicsEdit

CytoplasmEdit

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

NucleusEdit

During the primary oocyte stage of oogenesis, the nucleus is called a germinal vesicle[2]

The only normal human type of secondary oocyte has sex chromosomes 23,X (where sperm can be 23,X or 23,Y).

NestEdit

The space wherein an ovum or immature ovum is located is the cell-nest[3].

AbnormalitiesEdit

  • 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.

ReferencesEdit

  1. answers.com
  2. Biology-online
  3. Grier HJ, Uribe MC, Parenti LR (April 2007). Germinal epithelium, folliculogenesis, and postovulatory follicles in ovaries of rainbow trout, Oncorhynchus mykiss (Walbaum, 1792) (Teleostei, protacanthopterygii, salmoniformes). J. Morphol. 268 (4): 293–310.

Resources Edit

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 alsoEdit

External linksEdit

Preceded by:
None
Stages of human development
Oocyte
Succeeded by:
Zygote
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