Difference between revisions of "Polymorphism" - New World Encyclopedia
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In [[biology]], '''polymorphism''' (from [[Greek_language|Greek]]: ''poly'' "many", ''morph'' "form") can be defined as discontinuous [[genetic variation]] that results in the occurrence of several different forms or types of individuals among the members of a single species. The most obvious example of polymorphism is the separation of most higher organisms into male and female sexes. Another classic example is the different [[melanic]] and non-melanic [[Morph (zoology)|morphs]] of the [[peppered moth]]. A polymorphism that persists over many generations is usually maintained because no one form has an overall advantage or disadvantage over the others in terms of [[natural selection]]. The different forms are called morphs, which are the [[phenotype]] expression of an organism's [[genotype]]: the specific manifestation of a trait. Both natural and [[artificial selection]] cause different polymorphisms; they occur when organisms with different morphs reproduce with different degrees of success. | In [[biology]], '''polymorphism''' (from [[Greek_language|Greek]]: ''poly'' "many", ''morph'' "form") can be defined as discontinuous [[genetic variation]] that results in the occurrence of several different forms or types of individuals among the members of a single species. The most obvious example of polymorphism is the separation of most higher organisms into male and female sexes. Another classic example is the different [[melanic]] and non-melanic [[Morph (zoology)|morphs]] of the [[peppered moth]]. A polymorphism that persists over many generations is usually maintained because no one form has an overall advantage or disadvantage over the others in terms of [[natural selection]]. The different forms are called morphs, which are the [[phenotype]] expression of an organism's [[genotype]]: the specific manifestation of a trait. Both natural and [[artificial selection]] cause different polymorphisms; they occur when organisms with different morphs reproduce with different degrees of success. | ||
Revision as of 14:53, 14 March 2007
In biology, polymorphism (from Greek: poly "many", morph "form") can be defined as discontinuous genetic variation that results in the occurrence of several different forms or types of individuals among the members of a single species. The most obvious example of polymorphism is the separation of most higher organisms into male and female sexes. Another classic example is the different melanic and non-melanic morphs of the peppered moth. A polymorphism that persists over many generations is usually maintained because no one form has an overall advantage or disadvantage over the others in terms of natural selection. The different forms are called morphs, which are the phenotype expression of an organism's genotype: the specific manifestation of a trait. Both natural and artificial selection cause different polymorphisms; they occur when organisms with different morphs reproduce with different degrees of success.
Examples
In some cases of polymorphism, the different morphs are distinct. An example from botany is heterostyly, in which flowers occur in different forms having different arrangements of the pistil and the stamens. For instance, some cowslip plants (Primula veris) have "pin flowers", in which the style (the stalk of the pistil) reaches the end of the corolla tube and the stamens extend only halfway up the tube and thus are hidden. Other cowslip plants have "thrum flowers", in which the stamens reach the end of the corolla tube and the style is hidden inside. Also, thrum flowers produce bigger pollen grains than pin flowers. This polymorphism prevents inbreeding.
In other cases of polymorphism, there is continuous variation. For instance, normal human hair color, even within the single "habitat" of northern Europe, ranges continuously from black through reddish and brownish shades to nearly white. Little is known about any adaptive value of this polymorphism.
Another example of a polymorphic species is the Peppered moth.
Still other polymorphisms are variations in an organism's DNA sequence that may or may not affect its phenotype. Examples include single-nucleotide polymorphisms (SNPs) and restriction-fragment-length polymorphisms. Polymorphisms that do not affect the phenotype are sometimes called neutral polymorphisms.
See also
- CEPH
External link
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