This MedLibrary.org supplementary page on Apomixis is provided directly from the open source Wikipedia as a service to our readers. Please see the note below on authorship of this content, as well as the Wikipedia usage guidelines. To search for other content from our encyclopedia supplement, please use the form below:
Related Sponsors
In botany, apomixis (also called apogamy) is asexual reproduction, without fertilization. In plants with independent gametophytes (notably ferns), apomixis refers to the formation of sporophytes by parthenogenesis of gametophyte cells. Apomixis also occurs in flowering plants, where it is also called agamospermy. Apomixis in flowering plants mainly occurs in two forms: In agamogenesis (also called gametophytic apomixis), the embryo arises from an unfertilized egg that was produced without meiosis. In adventitious embryony , a nucellar embryo is formed from the surrounding nucellus tissue. Apomictically produced seeds are genetically identical to the parent plant.
As apomictic plants are genetically identical from one generation to the next, each has the characters of a true species, maintaining distinctions from other congeneric apomicts, while having much smaller differences than is normal between species of most genera. They are therefore often called microspecies. In some genera, it is possible to identify and name hundreds or even thousands of microspecies, which may be grouped together as aggregate species, typically listed in Floras with the convention "Genus species agg." (e.g., the bramble, Rubus fruticosus agg.). Examples of apomixis can be found in the genera Crataegus (hawthorns), Amelanchier (shadbush), Sorbus (rowans and whitebeams), Rubus (brambles or blackberries), Hieracium (hawkweeds) and Taraxacum (dandelions). Although the evolutionary advantages of sexual reproduction are lost, apomixis does pass along traits fortuitous for individual evolutionary fitness.
A unique example of male apomixis has recently been discovered in the Saharan Cypress, Cupressus dupreziana, where the seeds are derived entirely from the pollen with no genetic contribution from the female "parent" (Pichot, et al., 2000, 2001).
See also
- Parthenocarpy
- Parthenogenesis, the animal equivalent of apomixis.
References
- Gvaladze G.E. (1976). Forms of Apomixis in the genus Allium L. In: S.S. Khokhlov (Ed.): Apomixis and Breeding, Amarind Pub., New Delhi-Bombay-Calcutta-New York pp. 160-165
- Pichot, C., Fady, B., & Hochu, I. (2000). Lack of mother tree alleles in zymograms of Cupressus dupreziana A. Camus embryos. Ann. For. Sci. 57: 17–22.
Wikipedia content modification information:
- This page was last modified on 15 April 2008, at 16:00.
Wikipedia Authorship and Review
Wikipedia content provided here is not reviewed directly by MedLibrary.org. Wikipedia content is authored by an open community of volunteers and is not produced by or in any way affiliated with MedLibrary.org.
Wikipedia Usage Guidelines
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article on "Apomixis".
The URL for this specific entry is:
All Wikipedia text is available under the terms of the GNU Free Documentation License. (See Copyrights for details). Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc.