Expressivity
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2008-02-26T17:55:31Z
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{{Wikify|date=February 2008}}
{{Unreferenced|date=February 2008}}
'''Expressivity''' is a term used in [[genetics]] that refers to variations of a [[phenotype]] in individuals carrying a particular [[genotype]]. The term can be used to qualitatively or quantitatively characterize the extent of the phenotype variation given a particular genotype. The term is equivalent to the severity of a condition in clinical medicine. For example, the amount of blood ejected from the pumping heart with each contraction can be quantitated by echocardiography and is called the ejection fraction. If a specific genotype is associated with the development of congestive heart failure, the expressivity would be represented by the range of ejection fractions seen in patients that have that genotype. As a more qualitative example, the "blue" gene might have an expressivity of 25% for individuals that express the "blue" gene and appear light blue, and 75% for individuals that express the "blue" gene and appear dark blue. This differs from [[penetrance]] in that penetrance refers to the likelihood of the gene generating any phenotype at all, while expressivity refers to the influence of an expressed gene in individuals. ''Variable expressivity'' occurs when a phenotype is expressed to a different degree among individuals with the same genotype. For example, individuals with the same allele for gene involved in a quantitative trait like body height might have large variance (some are taller than others), making prediction of the phenotype from a particular genotype alone difficult. The expression of a phenotype may be modified by the effects of aging, other genetic loci or environmental factors.
==See also==
*[[Penetrance]]
*[[Allele]]
*[[Phenotype]]
*[[Genotype]]
*[[Mendelian inheritance]]
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[[Category:Population genetics]]
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