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20-September-2008 09:55:54 - Phenotype For a non-technical introduction to the topic, see Introduction to genetics. Individuals in the mollusk species Donax variabilis show diverse coloration and patterning in their phenotypes. Individuals in the mollusk species Donax variabilis show diverse coloration and patterning in their phenotypes. A phenotype is any observable characteristic of an organism, such as its morphology, development, biochemical or physiological properties, or behavior. Phenotypes result from the expression of an organism's genes as well as the influence of environmental factors and possible interactions between the two. The genotype of an organism are the inherited instructions it carries within its genetic code. Not all organisms with the same genotype look or act the same way, because appearance and behavior are modified by environmental and developmental conditions. Also in the same way, not all organisms that look alike necessarily have the same genotype. This genotype-phenotype distinction was proposed by Wilhelm Johannsen in 1911 to make clear the difference between an organism's hery and what that hery produces.12 The distinction is similar to that proposed by August Weismann, who distinguished between germ plasm hery and somatic cells the body. A more modern version is Francis Crick's Central dogma of molecular biology. Despite its seemingly straightforward definition, the concept of the phenotype has some hidden subtleties. First, most of the 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. So, by extension, the term phenotype must include characteristics that can be made visible by some technical procedure. Another extension adds behaviour to the phenotype since behaviours are also affected by both genotypic and environmental factors. Biston betularia morpha typica, the standard light-coloured Peppered Moth. Biston betularia morpha typica, the standard light-coloured Peppered Moth. Biston betularia morpha carbonaria, the melanic Peppered Moth, illustrating discontinuous variation. Biston betularia morpha carbonaria, the melanic Peppered Moth, illustrating discontinuous variation. Second, the phenotype is not simply a product of the genotype, but is influenced by the environment to a greater or lesser extent see also phenotypic plasticity. And, further, if the genotype is defined narrowly, then it must be remembered that not all hery is carried by the nucleus. For example, mitochondria transmit their own DNA directly, not via the nucleus, though they divide in unison with the nucleus. The phenotype is composed of traits or characteristics 3. Some phenotypes are controlled entirely by the individual's genes. Others are controlled by genes but are significantly affected by extragenetic or environmental factors. Almost all humans inherit the capacity to speak and understand language, but which language they learn is entirely an environmental matter. Phenotypic variation Phenotypic variation due to underlying heritable genetic variation is a fundamental prerequisite for evolution by natural selection. It is the living organism as a whole that contributes or not to the next generation, so natural selection affects the genetic structure of a population indirectly via the contribution of phenotypes. Without phenotypic variation, there would be no evolution by natural selection. 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 Genotypes often have great flexibility in the modification and expression of phenotypes, in many organisms these phenotypes are very different under varying environmental conditions. The plant Hieracium umbellatum is found growing in two different habitats in Sweden. One habitat is rocky, sea-side cliffs, where the plants are bushy with broad leaves and expanded inflorescences; the other is among sand dunes where the plants grow prostrate with narrow leaves and compact inflorescences. These habitats alternate along the coast of Sweden and the habitat that the seeds of Hieracium umbellatum land in, determine the phenotype that grows.4 An example of random variation in Drosophila flies is the number of ommatidia, which may vary randomly between left and right eyes 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 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 make 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 that may influence its chances of being replicated. These can be effects on the organism in which the gene resides, the environment, or other organisms. For instance, a beaver dam might be considered a phenotype of beaver genes, the same way beaver's powerful incisor teeth are phenotype expressions of their genes. Dawkins also cites the effect of an organism on the behaviour of another organism, such as the devoted nurturing of a cuckoo by a parent clearly of a different species as an example of the extended phenotype. The concept of phenotype can be extended to variations below the level of the gene that affect an organism's fitness. For example, silent mutations that do not change the corresponding amino acid sequence of a gene may change the frequency of guanine-cytosine base pairs GC content. These base pairs have a higher thermal stability melting point, see also DNA-DNA hybridization than adenine-thymine, a property that might convey, among organisms living in high-temperature environments, a selective advantage on variants enriched in GC content. References ^ Churchill F.B. 1974. William Johannsen and the genotype concept. J History of Biology 7, 5-30. ^ Johannsen W. 1911. The genotype conception of hery. American Naturalist 45, 129-159 ^ Sydney Brenner and Jeffrey H. Miller. 2002. Encyclopedia of Genetics San Diego: Academic Press. ^ Botany online: Evolution: The Modern Synthesis - Phenotypic and Genetic Variation; Ecotypes See also Phenome Genotype v d e The development of phenotype Key concepts Genotype-phenotype distinction · Norms of reaction · Gene-environment interaction · Heritability · Quantitative genetics Genetic architecture Dominance relationship · Epistasis · Polygenic inheritance · Pleiotropy · Plasticity · Canalisation · Fitness landscape Non-genetic influences Epigenetics · Maternal effect · Dual inheritance theory Developmental architecture Segmentation · Modularity Evolution of genetic systems Evolvability · Mutational robustness · Evolution of sex Influential figures C. H. Waddington · Richard Lewontin Debates Nature versus nurture List of evolutionary biology topics Retrieved from http://en..org/wiki/Phenotype Categories: Classical genetics Views Article Discussion this page History Personal tools Log in / create account Navigation Main page Contents Featured content Current events Random article Search Go Search Interaction Community portal Recent changes Contact Donate to Help Toolbox What links here Related changes Upload file Special pages Printable version Permanent link Cite this page Languages العربية БългарÑ?ки Català Česky Dansk Deutsch Eesti Español Esperanto Français Galego í•œêµì–´ Ido Bahasa Indonesia Italiano עברית Magyar МакедонÑ?ки Nederlands 日本語 Polski Português Română РуÑ?Ñ?кий Seeltersk Simple English SlovenÄ?ina СрпÑ?ки / Srpski Suomi Svenska Türkçe УкраїнÑ?ька ä¸æ–‡ This page was last modified on 8 August 2008, at 04:58
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