HOME

TheInfoList




In
genetics Genetics is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, ...

genetics
, expressivity is the degree to which a
phenotype In genetics Genetics is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular inter ...

phenotype
is expressed by individuals having a particular
genotype The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a specific ...
. (Alternately, it may refer to the
expression
expression
of particular
gene In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mecha ...

gene
by individuals having a certain phenotype.) Expressivity is related to the ''intensity'' of a given phenotype; it differs from
penetrancePenetrance in genetics Genetics is a branch of biology concerned with the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) Though heredity had been observed for millennia, Gregor Mendel, Moravia, Moravian sc ...
, which refers to the ''proportion'' of individuals with a particular genotype that actually express the phenotype.


Variable expressivity

Variable expressivity refers to the degree in which a genotype is phenotypically expressed. For example, multiple people with the same disease can have the same genotype but one may express more severe symptoms, while another carrier may appear normal. This variation in expression can be affected by modifier genes, epigenetic factors or the environment. Modifier genes can alter the expression of other genes in either an additive or multiplicative way. Meaning the phenotype that is observed can be a result of two different
alleles An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is one of two, or more, forms of a given gene In biology, a gene (from ''genos'' "...Wilhelm Johannsen coined the word gene to describe the Mendelian_inheritance ...
being summed or multiplied. However, a reduction in expression may also occur in which the primary
locus Locus (plural loci) is Latin for "place". It may refer to: Entertainment * Locus (comics), a Marvel Comics mutant villainess, a member of the Mutant Liberation Front * Locus (magazine), ''Locus'' (magazine), science fiction and fantasy magazine ...
, where the phenotype is expressed, is affected. Epigenetic factors, such as cis-regulatory elements, can also cause variability in expression by inducing variation in transcript abundance.


Examples

Three common syndromes that involved phenotypic variability due to expressivity include:
Marfan syndrome Marfan syndrome (MFS) is a rare multi-systemic genetic disorder A genetic disorder is a health problem caused by one or more abnormalities in the genome In the fields of molecular biology Molecular biology is the branch of bio ...
,
Van der Woude Syndrome Van der Woude syndrome (VDWS) is a genetic disorder characterized by the combination of lower congenital lip pits, lip pits, cleft lip with or without cleft palate (CL/P), and cleft palate only (CPO). The frequency of orofacial clefts ranges from 1 ...
, and
Neurofibromatosis Neurofibromatosis (NF) is a group of three conditions in which tumors A neoplasm () is a type of abnormal and excessive growth of Tissue (biology), tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth ...

Neurofibromatosis
. The characteristics of Marfan syndrome widely vary among individuals. The syndrome affects connective tissue in the body and has a spectrum of symptoms ranging from mild bone and joint involvement to severe neonatal forms and cardiovascular disease. This diversity in symptoms is a result of variable expressivity of the FBN1 gene found on chromosome 15 (see figure 1). The gene product is involved in the proper assembly of . Van der Woude syndrome is a condition that affects the development of the face, specifically a cleft lip (see figure 2), cleft palate or both . Carriers of the
mutation In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechan ...
can also have pits near the centre of the lower lip which may appear to be wet due to the presence of
salivary glands The salivary glands in mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'' ...
. The resulting phenotypes expressed varies significantly among individuals. This variation can range so broadly that a study published by the Department of Orthodontics at the University of Athens showed that some individuals were unaware that they possessed the genotype for this condition until they were tested. Neurofibromatosis (NF1),also known as Von Recklinghausen disease, is a
genetic disorder A genetic disorder is a health problem caused by one or more abnormalities in the genome In the fields of molecular biology Molecular biology is the branch of biology Biology is the natural science that studies life and li ...
that is caused by a mutation in the neurofibromin gene NF1 on chromosome 17. A
loss of function In biology, a mutation is an alteration in the base sequence, nucleotide sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA replication, DNA o ...
mutation in the
tumor suppressor gene A tumor suppressor gene (TSG), or anti-oncogene, is a gene In biology, a gene (from ''genos'' "...Wilhelm Johannsen coined the word gene to describe the Mendelian_inheritance#History, Mendelian units of heredity..." (Greek language, Greek) ...
can cause
tumors A neoplasm () is a type of abnormal and excessive growth of Tissue (biology), tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissu ...

tumors
on the nerves called
neurofibromas A neurofibroma is a benign nerve sheath tumor, nerve-sheath tumor in the peripheral nervous system. In 90% of cases, they are found as stand-alone tumors, while the remainder are found in persons with neurofibromatosis type I (NF1), an Genetic diso ...

neurofibromas
. These appear as small bumps under the skin. It is stipulated that the phenotypic variation is a result of unlinked genetic modifiers.


See also

*
Anticipation Anticipation is an emotion involving pleasure or anxiety in considering or awaiting an Expectation (epistemic), expected event. As a defence mechanism Robin Skynner considered anticipation as one of "the mature ways of dealing with real stress... ...
*
Pleiotropy Pleiotropy (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approxi ...
*
Mendelian inheritance Mendelian inheritance is a type of biological Biology is the natural science Natural science is a branch of science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific me ...

Mendelian inheritance
*
Genetic heterogeneityGenetic heterogeneity occurs through the production of single or similar phenotypes through different genetic mechanisms. There are two types of genetic heterogeneity: allelic heterogeneity, which occurs when a similar phenotype is produced by diffe ...
*
Haploinsufficiency Haploinsufficiency in genetics Genetics is a branch of biology concerned with the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) Though heredity had been observed for millennia, Gregor Mendel, Moravia, M ...


References


Further reading

* Population genetics {{genetics-stub