Information about Penetrance
Penetrance is a term used in genetics describing the proportion of individuals carrying a particular variation of a gene (the genotype) that also express a particular trait (the phenotype). For example, Huntingtons disease has 95% penetrance, whereby 5% of those with the dominant allele for Huntingtons don't acquire the disease and 95% do. Penetrance is the percentage of individuals with a specific genotype which possess an associated phenotype. For example, if 50% of the individuals carrying the "blue" gene are blue, the "blue" gene has 50% penetrance. Penetrance only considers whether individuals express the trait or not — for variation in the degree of expression of a given trait, see expressivity.
If a gene is highly penetrant, the trait it produces will always or almost always be apparent in an individual carrying the gene. Reduced or incomplete penetrance occurs when some individuals fail to express the trait, even though they carry the gene. A gene with low penetrance will only sometimes produce the symptom or trait with which it has been associated at a detectable level. In the case of low penetrance it is difficult to distinguish environmental from genetic factors.
Common examples used to show degrees of penetrance are often highly penetrant. There are several reasons for this:
However, relatively few of the genes in the genome show high penetrance. Traits such as height or intelligence are modified by multiple genes as well as by environmental factors. Distribution of polygenic traits often falls along a bell curve.
The penetrance of some diseases is age-related. An example is multiple endocrine neoplasia 1 (MEN 1), a disorder characterized by parathyroid hyperplasia and pancreatic islet-cell and pituitary adenomas. It is due to a mutation in the menin gene on chromosome 11q13. In one study the age-related penetrance of MEN1 was 7 percent by age 10 years and nearly 100 percent by age 60 years.
..... Click the link for more information.
If a gene is highly penetrant, the trait it produces will always or almost always be apparent in an individual carrying the gene. Reduced or incomplete penetrance occurs when some individuals fail to express the trait, even though they carry the gene. A gene with low penetrance will only sometimes produce the symptom or trait with which it has been associated at a detectable level. In the case of low penetrance it is difficult to distinguish environmental from genetic factors.
Common examples used to show degrees of penetrance are often highly penetrant. There are several reasons for this:
- Highly penetrant genes, and highly heritable symptoms, are easier to demonstrate – if the gene is present, the phenotype is expressed (recessivity, dominance, and co-dominance are fairly simple additions to this principle);
- Genes which are highly penetrant are more easily noticed by geneticists, and genes for symptoms which are highly heritable are more easily inferred to exist, and then more easily tracked down.
However, relatively few of the genes in the genome show high penetrance. Traits such as height or intelligence are modified by multiple genes as well as by environmental factors. Distribution of polygenic traits often falls along a bell curve.
The penetrance of some diseases is age-related. An example is multiple endocrine neoplasia 1 (MEN 1), a disorder characterized by parathyroid hyperplasia and pancreatic islet-cell and pituitary adenomas. It is due to a mutation in the menin gene on chromosome 11q13. In one study the age-related penetrance of MEN1 was 7 percent by age 10 years and nearly 100 percent by age 60 years.
See also
References
- Bessett JH et al. "Characterization of mutations in patients with multiple endocrine neoplasia type 1." Am J Hum Genet 1998 Feb;62(2):232-44.
Genetics is the science of heredity and variation in living organisms.[1][2] Knowledge of the inheritance of characteristics has been implicitly used since prehistoric times for improving crop plants and animals through selective breeding.
..... Click the link for more information.
..... Click the link for more information.
For a non-technical introduction to the topic, see .
A gene is a locatable region of genomic sequence, corresponding to a unit of inheritance, which is associated with regulatory regions, transcribed regions and/or other functional sequence regions...... Click the link for more information.
Genotype describes the genetic constitution of an individual, that is the specific allelic makeup of an individual, usually with reference to a specific character under consideration [1].
..... Click the link for more information.
..... Click the link for more information.
phenotype describes the total physical appearance of an organism, as opposed to its genotype. This genotype-phenotype distinction was proposed by Wilhelm Johannsen in 1911 to make clear the difference between an organism's heredity and what that heredity produces.
..... Click the link for more information.
..... Click the link for more information.
MeSH D006816 Huntington's disease (HD), also misspelt as Huntington disease and known historically as Huntington's chorea and chorea maior
..... Click the link for more information.
..... Click the link for more information.
Expressivity is a term used in genetics that refers to variations of a phenotype in individuals carrying a particular genotype. The term is used to qualitatively characterize the variance or extent of the phenotype given a particular genotype.
..... Click the link for more information.
..... Click the link for more information.
Bell curve can refer to:
..... Click the link for more information.
- Normal distribution, whose density function graph is a bell-shaped curve
- The Bell Curve, a book by Richard J. Herrnstein and Charles Murray that argued for a link between intelligence and race
..... Click the link for more information.
MeSH D009377 Multiple endocrine neoplasia (MEN) (or "multiple endocrine adenomas", or "multiple endocrine adenomatosis" -- "MEA") consists of three syndromes featuring tumors of endocrine glands, each with its own characteristic pattern.
..... Click the link for more information.
..... Click the link for more information.
The parathyroid glands are small endocrine glands in the neck, usually located behind the thyroid gland, which produce parathyroid hormone. In rare cases the parathyroid glands are located within the thyroid glands.
..... Click the link for more information.
..... Click the link for more information.
The pancreas is a gland organ in the digestive and endocrine systems of vertebrates<ref name="New Standard" />. It is both exocrine (secreting pancreatic juice containing digestive enzymes) and endocrine (producing several important hormones, including
..... Click the link for more information.
..... Click the link for more information.
The pituitary gland, or hypophysis, is an endocrine gland about the size of a pea that sits in a small, bony cavity (sella turcica) covered by a dural fold (sellar diaphragm) at the base of the brain.
..... Click the link for more information.
..... Click the link for more information.
Expressivity is a term used in genetics that refers to variations of a phenotype in individuals carrying a particular genotype. The term is used to qualitatively characterize the variance or extent of the phenotype given a particular genotype.
..... Click the link for more information.
..... Click the link for more information.
phenotype describes the total physical appearance of an organism, as opposed to its genotype. This genotype-phenotype distinction was proposed by Wilhelm Johannsen in 1911 to make clear the difference between an organism's heredity and what that heredity produces.
..... Click the link for more information.
..... Click the link for more information.
Genotype describes the genetic constitution of an individual, that is the specific allelic makeup of an individual, usually with reference to a specific character under consideration [1].
..... Click the link for more information.
..... Click the link for more information.
Mendelian inheritance (or Mendelian genetics or Mendelism) is a set of primary tenets relating to the transmission of hereditary characteristics from parent organisms to their children; it underlies much of genetics.
..... Click the link for more information.
..... Click the link for more information.
This article is copied from an article on Wikipedia.org - the free encyclopedia created and edited by online user community. The text was not checked or edited by anyone on our staff. Although the vast majority of the wikipedia encyclopedia articles provide accurate and timely information please do not assume the accuracy of any particular article. This article is distributed under the terms of GNU Free Documentation License.
Herod_Archelaus
