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Related to Incomplete penetrance: incomplete dominance, Variable penetrance


The proportion of individuals carrying a dominant gene in the heterozygous condition or a recessive gene in the homozygous condition in which the specific phenotypic effect is apparent. Also known as gene penetrance.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



a quantitative index of phenotypic variability in the expression of a gene. Penetrance is usually measured as the percent ratio of the number of individuals in whom the gene is expressed to the total number of individuals in whose genotype the gene is present in the homozygous state (for recessive genes) or heterozygous state (for dominant genes). Complete penetrance occurs when a certain gene is expressed in 100 percent of individuals with the appropriate genotype. Penetrance can also be incomplete, in which case it is called variable.

Variable penetrance is characteristic of the expressivity of many genes in humans, animals, plants, and microorganisms. For example, certain hereditary diseases of man develop only in a portion of the persons whose genotype contains the anomalous gene; in the remainder, the hereditary predisposition to the disease remains unrealized. Variable penetrance is due to the complexity and multistage nature of the many events that occur between the first actions of a gene on the molecular level and the eventual emergence of a trait. The penetrance of a gene may vary within broad limits, depending on the nature of the surrounding genes within the genotype. Strains of individuals with a given degree of penetrance may be obtained by artificial selection. The average degree of penetrance also depends on environmental conditions.


Lobashev, M. E. Genetika, 2nd ed. Leningrad, 1967.
Timofeev-Resovskii, N. V., and V. I. Ivanov. “Nekotorye voprosy fenogenetiki.” In the collection Aktual’nye voprosy sovremennoi genetiki. Moscow, 1966. Pages 114–30.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
The deformity is usually sporadic but may be inherited as an autosomal dominant trait with incomplete penetrance with 2:1 female to male ratio.
It is a matter of a sporadic disorder, though some authors suggest an autosomal dominant inheritance in some cases, with an incomplete penetrance and variable expressivity.
Half of the cases have a family history, whereas spontaneous mutation or incomplete penetrance is responsible for the other half.5 There is an equal distribution in both genders.
* Each child has a 50% risk of inheriting the predisposing mutation (not everyone with the mutation will develop cancer because of incomplete penetrance and gender-related expression).
This appeared to be transmitted as an autosomal dominant characteristic, with variable expression and incomplete penetrance. In these families, both in individuals with and without agenesis, other anomalies were present, such as supernumerary teeth, microdontia, and anomalous teeth.
The incomplete penetrance and the male propensity clearly indicate that the mtDNA mutation is not the only determinant for disease expression.
Penetrance is the likelihood a genetic trait will be expressed; in complete penetrance, all persons with the gene express the trait, but in incomplete penetrance, only a portion of the population with the gene expresses the genetic trait.
Familial benign pemphigus is a chronic autosomal dominant disorder with incomplete penetrance, which manifests clinically as vesicles and erythematous plaques with overlying crusts, which typically occur in the genital area, as well as the chest, neck, and axillary areas.
Rarely, patients with incomplete penetrance of the defective gene may have a completely normal magnetic resonance imaging study.
The gene appears to be autosomal dominant with incomplete penetrance, though the penetrance rate is close to 90%, said Garth Ehrlich, Ph.D., a coinvestigator at the institute.
In recent years, however, geneticists have begun to suspect that Hirschsprung's disease follows a pattern called autosomal dominance with incomplete penetrance. That's a fancy term for a simple concept: Some people get a copy of the gene and show no clinical signs of disease; others inherit one copy of this gene and get symptoms.
A gene that does not always cause symptoms is called incomplete penetrance. Sometimes the degree of penetrance (expression of symptoms) is different in males and females.

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