A phenotype () is the composite of an organism's observable characteristics or traits, such as its morphology, development, biochemical or physiological properties, phenology, behavior, and products of behavior (such as a bird's nest). A phenotype results from the expression of an organism's genes as well as the influence of environmental factors and the interactions between the two. When two or more clearly different phenotypes exist in the same population of a species, the species is called polymorph.
The genotype of an organism is the inherited instructions it carries within its genome.
This genotype-phenotype distinction was proposed by Wilhelm Johannsen in 1911 to make clear the difference between an organism's heredity and what that heredity produces. The distinction is similar to that proposed by August Weismann, who distinguished between germ plasm (heredity) and somatic cells (the body). The genotype-phenotype distinction should not be confused with Francis Crick's central dogma of molecular biology, which is a statement about the directionality of molecular sequential information flowing from DNA to protein, and not the reverse.
Richard Dawkins in 1978〔Dawkins 1978 http://onlinelibrary.wiley.com/doi/10.1111/j.1439-0310.1978.tb01823.x/abstract〕 and then again in his 1982 book ''The Extended Phenotype'' suggested that bird nests and other built structure such as caddis fly larvae cases and beaver dams can be considered as "extended phenotypes".
==Difficulties in definition==
Despite its seemingly straightforward definition, the concept of the phenotype has hidden subtleties. It may seem that anything dependent on the genotype is a phenotype, including molecules such as RNA and proteins. Most molecules and structures coded by the genetic material are not visible in the appearance of an organism, yet they are observable (for example by Western blotting) and are thus part of the phenotype. Human blood groups are an example. It may also seem that this goes beyond the original intentions of the concept with its focus on the (living) organism in itself, meaning that the lowest level of biological organization compatible with the phenotype concept is at the cellular level. Either way, the term phenotype includes traits or characteristics that can be made visible by some technical procedure. A notable extension to this idea is the presence of "organic molecules" or metabolites that are generated by organisms from chemical reactions of enzymes, e.g. vitamins, that can be scored as phenotype. Another extension adds behavior to the phenotype, since behaviors are also observable characteristics. Indeed, there is research into the clinical relevance of behavioral phenotypes as they pertain to a range of syndromes. Often, the term "phenotype" is incorrectly used as a shorthand to indicate ''phenotypical changes'' observed in mutated organisms (most often in connection with knockout mice).
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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