Phenotype information

 

An organism's phenotype (Greek phainein, 'to show', and typos, 'type'), is the composite of its observable characteristics or traits, such as morphology, development, biochemical or physiological properties, and behaviors, and products of behavior. A phenotype results from the expression of an organism's genetic code, its genotype, as well as the influence of environmental factors and interactions between the two (G x E = P). When two or more clearly different phenotypes exist in the same population of a species, that species is polymorphic.

 

Modern genotype-phenotype theory was first proposed by Wilhelm Johannsen in 1911 to make clear the difference between an organism's heredity and what that heredity produces. Wilhelm Johannsen first used the terms phenotype and genotype in his paper, Om arvelighed i samfund og i rene linier ("On heredity in society and in pure lines") and in his book Arvelighedslærens Elementer which was rewritten, as Elemente der exakten Erblichkeitslehre, introducing the term gene as coined in opposition to Darwin’s pangene.

 

The genotype-phenotype difference is similar to that proposed by August Weismann, who distinguished between germ plasm (heredity gametes) and somatic cells (body). Multicellular organisms consist of germ cells containing heritable information, and somatic cells that carry out ordinary bodily functions. The germ cells are primarily influenced, neither by environmental contingent, nor by learning, or somatic morphological changes that happen during the lifetime of an organism. Effects are therefore one-way, germ cells produce somatic cells and are not affected by anything somatic cells learn, nor retain any ability an individual acquires. Genetic information cannot pass from soma to germplasm and therefore on to the next generation individual.

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[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. “The Central Dogma states, that once 'information' has passed into protein it cannot get out again. The transfer of information from nucleic acid to nucleic acid, or from nucleic acid to protein may be possible, however transfer from protein to protein, or from protein to nucleic acid is impossible…” 1958]

 

Richard Dawkins in 1978 and in the 1982 book The Extended Phenotype suggested that bird nests and other built structures such as caddisfly larvae cases and beaver dams can be considered as "extended phenotypes". A phenotype that included all effects that a gene has on its surroundings, including other organisms, arguing that "An animal's behavior tends to maximize the survival of the genes 'for' that behavior, whether or not those genes happen to be in the body of the particular animal performing it." The main idea is that phenotype should not be limited to biological processes such as protein biosynthesis or tissue growth but extended to include all effects that a gene has on its environment, inside or outside the body of the individual organism.

 

Three elements of the extended phenotype

 

• 1.       Architectural constructions

• 2.       Manipulating other organisms

• 3.       Remote action on a host

 

[Not to forget the relevance of Richard Dawkins’s 1976 Selfish Gene and the idea of inclusive fitness over individual fitness, and connected to that social-psychological meme concept, as driven parallel to biological evolution, by variation, mutation, competition, and inheritance.]

 

Molecular extensions of phenotype include traits or characteristics which can be made visible by some technical procedure, extending to the idea of "organic molecules" or metabolites that are generated by organisms.

Phenotypic variation (due to underlying heritable genetic variation) is a fundamental prerequisite for evolution by natural selection.

 

The word phenome is sometimes used to refer to a collection of traits, while the simultaneous study of such a collection is referred to as phenomics. Phenomics is an important field of study because it can be used to figure out which genomic variants affect phenotypes which then can be used to explain things like health, disease, and evolutionary fitness.