Difference between revisions of "Phenotype" - New World Encyclopedia

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[[Image:Coquina variation3.jpg|thumb|right|260px|Individuals in the [[mollusk]] species [[Donax|''Donax variabilis'']] show diverse coloration and patterning in their phenotypes.]]
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The '''phenotype''' of an individual [[organism]] is either its total physical appearance and constitution or a specific manifestation of a [[Trait (biological)|trait]], such as size, eye color, or [[behavior]] that varies between individuals. Phenotype is determined to some extent by [[genotype]], or by the identity of the [[allele]]s that an individual carries at one or more positions on the [[chromosome]]s.  Many phenotypes are determined by multiple [[gene]]s and influenced by [[natural environment|environment]]al factors.  Thus, the identity of one or a few known alleles does not always enable prediction of the phenotype.
 
The '''phenotype''' of an individual [[organism]] is either its total physical appearance and constitution or a specific manifestation of a [[Trait (biological)|trait]], such as size, eye color, or [[behavior]] that varies between individuals. Phenotype is determined to some extent by [[genotype]], or by the identity of the [[allele]]s that an individual carries at one or more positions on the [[chromosome]]s.  Many phenotypes are determined by multiple [[gene]]s and influenced by [[natural environment|environment]]al factors.  Thus, the identity of one or a few known alleles does not always enable prediction of the phenotype.
  
 
Nevertheless, because phenotypes are much easier to observe than genotypes (it doesn't take chemistry or [[sequencing]] to determine a person's eye color), [[classical genetics]] uses phenotypes to deduce the functions of genes. Breeding experiments can then check these inferences.  In this way, early [[geneticists]] were able to trace inheritance patterns without any knowledge of [[molecular biology]].
 
Nevertheless, because phenotypes are much easier to observe than genotypes (it doesn't take chemistry or [[sequencing]] to determine a person's eye color), [[classical genetics]] uses phenotypes to deduce the functions of genes. Breeding experiments can then check these inferences.  In this way, early [[geneticists]] were able to trace inheritance patterns without any knowledge of [[molecular biology]].
  
The interaction between genotype and phenotype has often been described using a simple equation:
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Phenotypic variation (due to underlying heritable [[genetic variation]]) is a fundamental prerequisite for [[evolution]] by [[natural selection]]. The [[fitness (biology) | fitness]] of an organism is a high-level phenotype determined by the contributions of thousands of more specific phenotypes. Without phenotypic variation, individual organisms would all have the same fitness, and changes in phenotypic frequency would proceed without any selection (randomly).
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The interaction between genotype and phenotype has often been conceptualized by the following relationship:
  
 
:'''genotype + environment → phenotype'''
 
:'''genotype + environment → phenotype'''
  
A slightly more nuanced version of the equation is:
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A slightly more nuanced version of the relationships is:
  
 
:'''genotype + environment + random-variation → phenotype'''
 
:'''genotype + environment + random-variation → phenotype'''
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A phenotype is any detectable characteristic of an [[organism]] (i.e., structural, biochemical, physiological and behavioral) determined by an interaction between its [[genotype]] and environment (see [[genotype-phenotype distinction]] and [[phenotypic plasticity]] for a further elaboration of this distinction).
 
A phenotype is any detectable characteristic of an [[organism]] (i.e., structural, biochemical, physiological and behavioral) determined by an interaction between its [[genotype]] and environment (see [[genotype-phenotype distinction]] and [[phenotypic plasticity]] for a further elaboration of this distinction).
  
The idea of the phenotype has been generalized by [[Richard Dawkins]] to include effects on other organisms or the environment in ''[[The Extended Phenotype]]''.
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According to the [[autopoiesis|autopoietic]] notion of living systems by [[Humberto Maturana]], the phenotype is epigenetically being constructed throughout [[ontogeny]], and we as observers do the distinctions that define any particular trait at any particular state of the organism's life cycle.
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The idea of the phenotype has been generalized by [[Richard Dawkins]] (in ''[[The Extended Phenotype]]'') to mean all the effects a [[gene]] has on the outside world which may influence its chances of being replicated.  These can be effects on the organism in which the gene resides, the environment or other organisms.
  
 
{{genarch}}
 
{{genarch}}
  
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[[Category:Life sciences]]
 
[[Category:Life sciences]]

Revision as of 21:12, 29 November 2006

Individuals in the mollusk species Donax variabilis show diverse coloration and patterning in their phenotypes.

The phenotype of an individual organism is either its total physical appearance and constitution or a specific manifestation of a trait, such as size, eye color, or behavior that varies between individuals. Phenotype is determined to some extent by genotype, or by the identity of the alleles that an individual carries at one or more positions on the chromosomes. Many phenotypes are determined by multiple genes and influenced by environmental factors. Thus, the identity of one or a few known alleles does not always enable prediction of the phenotype.

Nevertheless, because phenotypes are much easier to observe than genotypes (it doesn't take chemistry or sequencing to determine a person's eye color), classical genetics uses phenotypes to deduce the functions of genes. Breeding experiments can then check these inferences. In this way, early geneticists were able to trace inheritance patterns without any knowledge of molecular biology.

Phenotypic variation (due to underlying heritable genetic variation) is a fundamental prerequisite for evolution by natural selection. The fitness of an organism is a high-level phenotype determined by the contributions of thousands of more specific phenotypes. Without phenotypic variation, individual organisms would all have the same fitness, and changes in phenotypic frequency would proceed without any selection (randomly).

The interaction between genotype and phenotype has often been conceptualized by the following relationship:

genotype + environment → phenotype

A slightly more nuanced version of the relationships is:

genotype + environment + random-variation → phenotype

An example of the importance of random variation in phenotypic expression is Drosophila flies in which number of eyes may vary (randomly) between left and right sides in a single individual as much as they do between different genotypes overall, or between clones raised in different environments.

A phenotype is any detectable characteristic of an organism (i.e., structural, biochemical, physiological and behavioral) determined by an interaction between its genotype and environment (see genotype-phenotype distinction and phenotypic plasticity for a further elaboration of this distinction).

According to the autopoietic notion of living systems by Humberto Maturana, the phenotype is epigenetically being constructed throughout ontogeny, and we as observers do the distinctions that define any particular trait at any particular state of the organism's life cycle.

The idea of the phenotype has been generalized by Richard Dawkins (in The Extended Phenotype) to mean all the effects a gene has on the outside world which may influence its chances of being replicated. These can be effects on the organism in which the gene resides, the environment or other organisms.

Template:Genarch

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