Asexual reproduction
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Asexual reproduction (also known as agamogenesis) is a form of reproduction which does not involve meiosis, haploid formation, or fertilization. In laymen's terms, there is only one "cell" involved. This form of reproduction is common among simple organisms such as amoeba, bacteria, and other single-celled organisms, and most plants reproduce asexually as well (see vegetative reproduction).
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[edit] Advantages
Because it does not require male participation, asexual reproduction occurs faster than sexual reproduction and requires less energy. Additionally, asexual reproduction produces an exact replica of the parent because of the lack of genetic recombination. From an evolutionary standpoint, one could thus argue that asexual reproduction is inferior because it stifles the potential for change. However, there is also a significantly reduced chance of mutation or other complications that can result from the mixing of genes.
A 2004 article in the journal Nature reported that the modern arbuscular mycorrhizas fungi, which reproduces asexually, is identical to fossils records dating back to the Ordovician period, 460 million years ago.[1]
[edit] Types of asexual reproduction
Many, but not all, single-celled organisms reproduce asexually through binary fission. Some single-celled organisms rely on one or more host organisms in order to reproduce, but most literally divide into two organisms. An exception to the rule are ciliates, which reproduce both sexually and asexually. All prokaryotes (the vast majority of which are unicellular) reproduce asexually. [citation needed]
There are three types of asexual reproduction utilized by plants: regeneration, vegetative reproduction, and spore formation. The last type, spore formation, involves the production of reproductive cells called spores that contain DNA and develop into a new organism after dispersal. This method of reproduction is found in the ferns, and involves sporogenesis without meiosis. Thus the chromosome number of the spore cell is the same as that of the parent producing the spores.
[edit] Examples in higher organisms
- The cape bee Apis mellifera capensis is known to sometimes reproduce asexually through a process called thelytoky.
- A number of insects, notably aphids can alternate between sexual and asexual reproduction. Under favourable conditions, aphids will produce eggs that have not gone through meiosis, essentially cloning itself.
- In the absence of a male, female Turkeys are known to produce fertile eggs. The individual produced is often sickly, and nearly always male. This behaviour can interfere with the incubation of eggs in Turkey farming[2].
- In the film Jurassic Park it is stated that some species of frogs have been known to reproduce asexually. While some forms of frogs have been known to change gender, they would still need to find a frog of the opposite gender in order to have fertilized eggs.
[edit] Notes
- ^ Teresa Pawlowska and John Taylor, "Organization of genetic variation in individuals of arbuscular mycorrhizal fungi", Nature, 2004, volume 427 (6976), pages 733-737.
- ^ Savage, Thomas F. (September 12, 2005). A Guide to the Recognition of Parthenogenesis in Incubated Turkey Eggs. Oregon State University. Retrieved on 2006-10-11.
[edit] External links
[edit] References
- Graham, L., J. Graham, & L. Wilcox. 2003. Plant Biology. Pearson Education, Inc., Upper Saddle River, N.J.: pp. 258-259.
