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Related to Variable penetrance: 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 ?
The inheritance of TSC is an autosomal dominant trait with variable penetrance.
Approximately half of AC cases are considered to be familial, most frequently in an autosomal-dominant fashion with variable penetrance.
Although family history is not remarkable in this case, variable penetrance is often considered in patients with HCP, especially in fertile women in whom female hormones are known to be a predisposing factor.
Although long QT syndrome runs in families, there may be significant variations in clinical features among family members due to variable penetrance (differing frequency of manifestation of genetic traits by individuals).
Denborough concluded that this indicated that there was variable penetrance of the disease or that some patients could tolerate light anaesthesia (4).
However, as many of these disorders have variable penetrance and fluctuate in an individual woman over time it should be noted that:
There are reports in the literature linking the disease to genetic factors, with an autosomal dominant pattern of transmission with variable penetrance.
INTRODUCTION: Porokeratosis is an autosomal dominant genodermatosis with variable penetrance, characterized by a clonal disorder of keratinization with one or more atrophic patches surrounded by a clinically and histologically distinctive hyperkeratotic ridge like border called the cornoid lamella.
The challenge in arriving at appropriate diagnosis and treatment comes from the variable penetrance of A1AT genetic defects and the limitations of each test.
Primary HOA is rare and often familial, transmitted as autosomal dominant with variable penetrance.

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