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Related to Penetrance: expressivity, Incomplete 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.



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.


References in periodicals archive ?
This certainty is described as 100 percent penetrance.
Di Fonzo and his colleagues also identified some asymptomatic carriers--a finding that suggests penetrance was reduced or was age dependent.
Generally BRCA2 mutation penetrance for lifetime risk of breast cancer is lower than for BRCA1 mutation carriers, resulting in a later age of onset.
I know of no other condition that predicts Parkinson's disease with that high a degree of penetrance," he said.
It is widely accepted that the disease occurs secondary to a dominant gene that shows poor penetrance and is intimately linked to histocompatibility antigens HLA-A3, HLA-B7, and HLA-B14.
A consensus conference convened in 1997 by the Centers for Disease Control and Prevention and the National Human Genome Research Institute did not recommend genetic testing, although it did urge that high priority be given to population-based research to clarify issues such as age- and sex-related penetrance of genotypes and the psychosocial implications of screening (JAMA 280[2]:172-78, 1998).
However, because of genetic phenomena known as incomplete penetrance and variable expressivity, most Waardenburg's patients do not exhibit all of the syndrome's characteristic traits.
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