Phenotype

The phenotype of an individual organism is either its total physical appearance and constitution, or a specific manifestation of a trait, such as size or eye color, 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.

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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 whatsoever of molecular biology.

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The interaction between genotype and phenotype has often been described using a simple equation:

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:genotype + environment ? phenotype

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A slightly more nuanced version of the equation is:

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:genotype + environment + random-variation ? phenotype

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

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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).

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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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Organism: In biology and ecology, an organism (in Greek organon = instrument) is an assembly of organs that influence each other in such a way that they function as a more or less stable whole and have properties of life....

Trait: In biology, a trait or character is a genetically inherited feature of an organism. As synonym for trait can be sometimes used the term phenotype; the difference is that this second term can also indicate the total physical appeareance or constitution....

Genotype: The genotype is the specific genetic makeup (the specific genome) of an individual, usually in the form of DNA. It codes for the phenotype of that individual....