An 'oocyte', 'ovocyte', or rarely 'oöcyte', is a female
gametocyte or
germ cell involved in
reproduction. In other words, it is an
immature ovum.
Formation
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.
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
[2]
The only normal 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''
[3].
Abnormalities
★
nondisjunction -- a failure of proper homolog separation in meiosis I, or sister
chromatid separation in meisosis 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 advance maternal age.
★ Some oocytes have multiple
nuclei, although it is thought they never mature.
References
1. answers.com
2. Biology-online
3. Germinal epithelium, folliculogenesis, and postovulatory follicles in ovaries of rainbow trout, Oncorhynchus mykiss (Walbaum, 1792) (Teleostei, protacanthopterygii, salmoniformes)
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
★
Slide
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