Expressivity
Encyclopedia
Expressivity is a term used in genetics
to refer to variations in a phenotype
among individuals carrying a particular genotype
. The term can be used to characterize qualitatively or quantitatively the extent of phenotypic variation given a particular genotype. The term is analogous 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 quantified 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. Expressivity is measured only when there is 100% penetrance.
This differs from penetrance
, which refers to the likelihood of the gene generating its associated phenotype at all, as determined by the proportion of individuals with a given genotype who also possess the associated phenotype. In contrast, expressivity refers to the influence of an expressed gene at the level of particular 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 a 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.
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
to refer to variations in a phenotype
Phenotype
A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
among individuals carrying a particular genotype
Genotype
The genotype is the genetic makeup of a cell, an organism, or an individual usually with reference to a specific character under consideration...
. The term can be used to characterize qualitatively or quantitatively the extent of phenotypic variation given a particular genotype. The term is analogous to the severity of a condition in clinical medicine
Clinical Medicine
Clinical Medicine is a peer-reviewed medical journal published bimonthly by the Royal College of Physicians. It was established in 1966 as the Journal of the Royal College of Physicians of London. It was doubly named between 1998 and 2000, and since 2001 it has appeared as Clinical Medicine. Its...
. For example, the amount of blood ejected from the pumping heart with each contraction can be quantified by echocardiography
Echocardiography
An echocardiogram, often referred to in the medical community as a cardiac ECHO or simply an ECHO, is a sonogram of the heart . Also known as a cardiac ultrasound, it uses standard ultrasound techniques to image two-dimensional slices of the heart...
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
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
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. Expressivity is measured only when there is 100% penetrance.
This differs from penetrance
Penetrance
Penetrance in genetics is the proportion of individuals carrying a particular variant of a gene that also express an associated trait . In medical genetics, the penetrance of a disease-causing mutation is the proportion of individuals with the mutation who exhibit clinical symptoms...
, which refers to the likelihood of the gene generating its associated phenotype at all, as determined by the proportion of individuals with a given genotype who also possess the associated phenotype. In contrast, expressivity refers to the influence of an expressed gene at the level of particular 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
Allele
An allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...
for a 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
- PenetrancePenetrancePenetrance in genetics is the proportion of individuals carrying a particular variant of a gene that also express an associated trait . In medical genetics, the penetrance of a disease-causing mutation is the proportion of individuals with the mutation who exhibit clinical symptoms...
- AlleleAlleleAn allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...
- PhenotypePhenotypeA phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
- GenotypeGenotypeThe genotype is the genetic makeup of a cell, an organism, or an individual usually with reference to a specific character under consideration...
- Mendelian inheritanceMendelian inheritanceMendelian inheritance is a scientific description of how hereditary characteristics are passed from parent organisms to their offspring; it underlies much of genetics...
- PleiotropyPleiotropyPleiotropy occurs when one gene influences multiple phenotypic traits. Consequently, a mutation in a pleiotropic gene may have an effect on some or all traits simultaneously...
- Genetic heterogeneityGenetic heterogeneityGenetic Heterogeneity is a phenomenon in which a single phenotype or genetic disorder may be caused by any one of a multiple number of alleles or non-allele mutations. This is in contrast to pleiotropy, where a single gene may cause multiple phenotypic expressions or disorders...