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What are the different ways a genetic condition can be inherited? From Genetics Home Reference. These conditions are usually inherited in one of several patterns, depending on the gene involved: Patterns of inheritance Inheritance pattern Description Examples Autosomal dominant One altered copy of the gene in each cell is sufficient for a person to be affected by an autosomal dominant disorder.
Huntington disease , Marfan syndrome Autosomal recessive In autosomal recessive inheritance , variants occur in both copies of the gene in each cell. Y chromosome infertility , some cases of Swyer syndrome Codominant In codominant inheritance , two different versions alleles of a gene are expressed, and each version makes a slightly different protein. ABO blood group, alpha-1 antitrypsin deficiency Mitochondrial Mitochondrial inheritance , also known as maternal inheritance, applies to genes in mitochondrial DNA.
Leber hereditary optic neuropathy LHON Many health conditions are caused by the combined effects of multiple genes described as polygenic or by interactions between genes and the environment. Topics in the Inheriting Genetic Conditions chapter What does it mean if a disorder seems to run in my family? Why is it important to know my family health history?
If a genetic disorder runs in my family, what are the chances that my children will have the condition? What are reduced penetrance and variable expressivity? Donna Krasnewich, M. Featured Content. Introduction to Genomics. Penetrance and expressivity ought to be considered. Sugar intolerance: galactose, fructose, saccharose, lactose. Most amino acid disorders : phenylketonuria, tyrosinosis, cystinosis, leucinosis. Wilson disease. Several disorders of hormono synthesis, mainly thyroid and adrenal.
Sickle cell anemia, Thalassemia. In the paternal progeny all individuals are normal. In the maternal progeny one often finds affected brothers or male sibs.
Usually affected individuals are male. In the affected sibship , one male out of two is affected, and one female out of two is carrier. Particular cases: I. All girls are normal but are HEZ carriers. One boy out of two is affected. Normal girls are HEZ. Girls can be affected. Situation not likely to happen for a rare gene, but more frequent if the gene frequency is high ex: colour blindness.
Remarks: to detect heterozygote carriers for genetic counseling. The number of individuals who carry a mutation is less than the number of individuals who have an abnormal phenotype. This is a quantitative estimate.
An improved method to evaluate mutations in those families will allow us to better understand this notion of penetrance. C not to confound an isolate case due to a reduced penetrance with a sporadic case due to a mutation. This a variable expressivity of the deleterious gene. It is a qualitative evaluation. In Marfan syndrome for an identical familial gene mutation, some individuals will have a severe form of the disease affecting the cardio-vascular, ocular and skeletal systems while for other individuals only the tall stature and arachnodactyly, without lens dislocation or aortic aneurysm, will be noted.
With each pregnancy, a woman who carries an altered gene for X-linked recessive has a 50 percent chance of having sons who are affected and a 50 percent chance of having daughters who carry one copy of the altered gene. Females with one gene variant associated with an X-linked recessive disorder typically have no or very mild signs or symptoms of the condition. X-linked: Because the inheritance pattern of many X-linked disorders is not clearly dominant or recessive, some experts suggest that conditions be considered X-linked rather than X-linked dominant or X-linked recessive.
As above, the probability of passing on an X-linked disorder differs between men and women. The sons of a man with an X-linked disorder will not be affected, but all of his daughters will inherit the altered gene and may develop signs and symptoms of the condition. Therefore, with each pregnancy, a woman with an X-linked disorder has a 50 percent chance of having a child with the altered gene.
An affected daughter may have milder signs and symptoms than an affected son. Y-linked inheritance: Because only males have a Y chromosome, only males can be affected by and pass on Y-linked disorders. All sons of a man with a Y-linked disorder will inherit the condition from their father. Codominant inheritance: In codominant inheritance , each parent contributes a different version of a particular gene, and both versions influence the resulting genetic trait.
The chance of developing a genetic condition with codominant inheritance, and the characteristic features of that condition, depend on which versions of the gene are passed from parents to their child.
Mitochondrial inheritance: Mitochondria, which are the energy-producing centers inside cells, each contain a small amount of DNA. Disorders with mitochondrial inheritance result from variants in mitochondrial DNA. Although these disorders can affect both males and females, only females can pass variants in mitochondrial DNA to their children.
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