Trait (biology)
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{{dablink|This article refers to traits in biology. For other uses of the term, see [[trait]]}}
A '''trait''' is a distinct [[phenotype|phenotypic]] character of an organism that may be inherited, environmentally determined or somewhere in between.<ref name=Lawrence>Lawrence, Eleanor (2005) ''Henderson's Dictionary of Biology''. Pearson, Prentice Hall. ISBN 0-13-127384-1</ref> For example, [[eye color]] is a ''character'', while blue, brown and hazel are ''traits''.
== Definition ==
A trait may be any single feature or quantifiable measurement of an organism. However, the most useful traits for [[genetic analysis]] are present in different forms in different individuals.
A visible trait is the final product of many [[Molecular Biology|molecular]] and [[Biochemistry|biochemical]] processes. In most cases, information starts with [[DNA]] traveling to [[RNA]] and finally to [[protein]] (ultimately affecting organism structure and function). This is the [[Central Dogma]] of [[molecular biology]] as stated by [[Francis Crick]].
This information flow may also be followed through the [[cell (biology)|cell]] as it travels from the [[DNA]] in the [[cell nucleus|nucleus]], to the [[Cytoplasm]], to the [[Ribosomes]] and the [[Endoplasmic Reticulum]], and finally to the [[Golgi Apparatus]], which may package the final products for export outside the cell.
Cell products are released into the [[biological tissue|tissue]], and [[organ (anatomy)|organ]]s of an [[organism]], to finally affect the [[physiology]] in a way that produces a trait.
==Genetic origin of traits in diploid organisms==
The heritable unit that may influence a trait is called a [[gene]]. A gene is a strand of [[DNA]] that is part of a very long and [[histone|compacted]] string of [[DNA]] called a [[chromosome]]. An important reference point along this string is the [[centromere]]; the distance from a gene to the centromere is referred to as the gene's [[locus (genetics)|locus]] or map location. A chromosomal region known to control a trait while the responsible gene within not being identified is referred to as a [[quantitative trait locus]].
The nucleus of a diploid cell contains two of each chromosome, with [[homology (biology)|homologous]] (mostly identical) pairs of chromosomes having the same genes at the same [[Locus (genetics)|loci]].
==Mendelian expression of genes in diploid organisms==
A gene is only a [[genetic code|DNA code]] sequence; the slightly different variations of that sequence are called alleles. [[Allele]]s can be significantly different and produce different product [[RNA]]s.
Combinations of different [[alleles]] thus go on to generate different traits through the [[Central Dogma|information flow]] charted above. For example, if the alleles on homologous [[chromosome]]s exhibit a "simple dominance" relationship, the trait of the "dominant" allele shows in the phenotype.
[[Gregor Mendel]] pioneered modern genetics. His most famous analyses were based on clear-cut traits with simple dominance. He determined that the [[inheritance|heritable]] units, what he called "[[gene]]s", occurred in pairs and could exhibit [[genetic linkage|linkage]]. His tool was [[statistics]]: long before the molecular model of [[DNA]] was introduced by [[James D. Watson]] and [[Francis Crick]].
Some examples of Inherited genes include eye color.
==Biochemistry of dominance and extensions to expression of traits==
The [[biochemistry]] of the intermediate [[proteins]] determines how they interact in the cell. Therefore, biochemistry [[Philosophy of Science|predicts]] how combinations of different alleles will produce varying traits.
Extended expression patterns seen in diploid organisms include facets of [[incomplete dominance]], [[codominance]], and [[multiple alleles]].
==See also==
*[[Character displacement]]
*[[Skill]]
==References==
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[[Category:Classical genetics]]
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