What is the difference between penetrance and expressivity?

Asked By: Santusa Francioni | Last Updated: 2nd February, 2020
Category: science genetics
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The main difference between penetrance and expressivity is that penetrance is a quantitative measurement, describing the levels of expression of a particular phenotype, which corresponds to a dominant genotype whereas expressivity is the extent of a given genotype expressed at the phenotypic level.

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Correspondingly, what is penetrance and expressivity?

“Complete” penetrance means the gene or genes for a trait are expressed in all the population who have the genes. Expressivity on the other hand refers to variation in phenotypic expression when an allele is penetrant. Back to the polydactyly example, an extra digit may occur on one or more appendages.

Also Know, what does penetrance mean in genetics? Penetrance in genetics is the proportion of individuals carrying a particular variant (or allele) of a gene (the genotype) that also express an associated trait (the phenotype). Common examples used to show degrees of penetrance are often highly penetrant.

Also Know, what does expressivity mean in genetics?

Definition. It describes the phenomenon of differing clinical features or phenotype among individuals carrying the same gene allele or genotype. Expressivity differs from penetrance, which describes the probability that a genetic variation (or allele) will yield the phenotype at all.

How do you calculate penetrance in genetics?

Crude penetrance estimates can be derived by dividing the observed number of diseased (penetrant) individuals by the number of obligate carriers (penetrant as well as obligate non-penetrant, that is, normal individuals with several affected offspring or normal individuals with affected parent and child).

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What causes penetrance?

Penetrance refers to the proportion of people with a particular genetic change (such as a mutation in a specific gene) who exhibit signs and symptoms of a genetic disorder. If some people with the mutation do not develop features of the disorder, the condition is said to have reduced (or incomplete) penetrance.

Are phenotypes always visible?

A phenotype is defined as the total make up of our physical characteristics. This means anything that affects us physically- it can be our hair or eye colour which is visible, or it could be our resistance to diseases, which is not.

What does incomplete penetrance mean?

Penetrance refers to the likelihood that a clinical condition will occur when a particular genotype is present. A condition is said to show incomplete penetrance when some individuals who carry the pathogenic variant express the associated trait while others do not.

What are Phenocopies give specific examples?

For example, a phenocopy is observed in Himalayan rabbits which have a white colored coat along with a black tail, nose, and ears when raised in moderate temperatures. However, when raised in colder climates, they develop phenotypically similar to genetically different black coated rabbits.

What causes incomplete penetrance?


Incomplete penetrance may be due to the effect of the type of mutation. Some mutations of a given disease may exhibit complete penetrance, where as others in the same gene show incomplete or very low penetrance. Reduced penetrance in some genetic disorders may also depend on genetic background of gene carriers.

What is Phenocopy in biology?

A phenocopy is a variation in phenotype (generally referring to a single trait) which is caused by environmental conditions (often, but not necessarily, during the organism's development), such that the organism's phenotype matches a phenotype which is determined by genetic factors.

What is a Haploinsufficient gene?

Haploinsufficiency: A situation in which the total level of a gene product (a particular protein) produced by the cell is about half of the normal level and that is not sufficient to permit the cell to function normally. One of the two copies of the gene may be missing due to a deletion.

What do modifier genes do?

Modifier genes encode products which can alter the expression or function of another gene or its product. Modifiers can therefore operate at many levels, modifying transcriptional efficiency, translation or protein function (Fig. 2.3).

What is Codominance in biology?

Codominance occurs when two versions, or “alleles,” of the same gene are present in a living thing, and both are expressed. Instead of one trait being dominant over the other, both traits appear. Codominance also occurs in some less visible traits, such as blood type.

What is gene interaction?


In genetics, gene-gene interaction (epistasis) is the effect of one gene on a disease modified by another gene or several other genes. Epistasis can be contrasted with dominance, which is an interaction between alleles at the same gene locus.

What is autosomal dominant inheritance?

Dominant inheritance means an abnormal gene from one parent can cause disease. This disease can also occur as a new condition in a child when neither parent has the abnormal gene. A parent with an autosomal dominant condition has a 50% chance of having a child with the condition.

What is an allelic mutation?

From Wikipedia, the free encyclopedia. Allelic heterogeneity is the phenomenon in which different mutations at the same locus lead to the same or very similar phenotypes. These allelic variations can arise as a result of natural selection processes, as a result of exogenous mutagens, genetic drift, or genetic migration

What is the expressivity of a disease referring to?

Expressivity measures the extent to which a genotype exhibits its phenotypic expression. Just as individuals with a certain mutation can exhibit differences in disease severity, they can also show differences in many other aspects of their phenotypes, such as their age of onset of disease symptoms.

What is polygenic inheritance?

Polygenic inheritance occurs when one characteristic is controlled by two or more genes. Often the genes are large in quantity but small in effect. Examples of human polygenic inheritance are height, skin color, eye color and weight. Polygenes exist in other organisms, as well.

What are multiple alleles?


multiple alleles Three or more alternative forms of a gene (alleles) that can occupy the same locus. However, only two of the alleles can be present in a single organism. For example, the ABO system of blood groups is controlled by three alleles, only two of which are present in an individual. A Dictionary of Biology.

What is Hemizygous?

Hemizygous is a condition in which only one copy of a gene or DNA sequence is present in diploid cells. Males are hemizygous for most genes on sex chromosomes, having only one X and one Y chromosome.

What does wild type mean in genetics?

Wild type (WT) refers to the phenotype of the typical form of a species as it occurs in nature. Originally, the wild type was conceptualized as a product of the standard "normal" allele at a locus, in contrast to that produced by a non-standard, "mutant" allele.