Examples Autosomal dominant One mutated copy of the gene in each cell is sufficient for a person to be affected by an autosomal dominant disorder. In some cases, an affected person inherits the condition from an affected parent. In others, the condition may result from a new mutation in the gene and occur in people with no history of the disorder in their family. Huntington disease , Marfan syndrome Autosomal recessive In autosomal recessive inheritance , both copies of the gene in each cell have mutations.
The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition. Autosomal recessive disorders are typically not seen in every generation of an affected family.
In females who have two X chromosomes , a mutation in one of the two copies of the gene in each cell is sufficient to cause the disorder. In males who have only one X chromosome , a mutation in the only copy of the gene in each cell causes the disorder.
In most cases, males experience more severe symptoms of the disorder than females. A characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons no male-to-male transmission. In males who have only one X chromosome , one altered copy of the gene in each cell is sufficient to cause the condition.
In females who have two X chromosomes , a mutation would have to occur in both copies of the gene to cause the disorder. Because it is unlikely that females will have two altered copies of this gene, males are affected by X-linked recessive disorders much more frequently than females. Because only males have a Y chromosome, in Y-linked inheritance, a mutation can only be passed from father to son. 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.
Both alleles influence the genetic trait or determine the characteristics of the genetic condition. ABO blood group, alpha-1 antitrypsin deficiency Mitochondrial Mitochondrial inheritance , also known as maternal inheritance, applies to genes in mitochondrial DNA. Mitochondria, which are structures in each cell that convert molecules into energy, each contain a small amount of DNA. Because only egg cells contribute mitochondria to the developing embryo, only females can pass on mitochondrial mutations to their children.
Conditions resulting from mutations in mitochondrial DNA can appear in every generation of a family and can affect both males and females, but fathers do not pass these disorders to their daughters or sons. 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. Such disorders usually do not follow the patterns of inheritance listed above.
For more information, please see What are complex or multifactorial disorders? Disorders caused by changes in the number or structure of chromosomes also do not follow the straightforward patterns of inheritance listed above. To read about how chromosomal conditions occur, please see Are chromosomal disorders inherited? Other genetic factors sometimes influence how a disorder is inherited.
For an example, please see What are genomic imprinting and uniparental disomy? For more information about inheritance patterns: The Centre for Genetics Education provides information about many of the inheritance patterns outlined above: