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IMG Home Autosomal dominant inheritance pattern. Legal Conditions and Terms Any use of this site constitutes your agreement to the Terms and Conditions and Privacy Policy linked below. Advertising Mayo Clinic is a nonprofit organization and proceeds from Web advertising help support our mission. 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 variant 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 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.
X-linked disorders are caused by variants in genes on the X chromosome , one of the two sex chromosomes in each cell. In males who have only one X chromosome , an alteration in the only copy of the gene in each cell is sufficient to cause the condition. In females who have two X chromosomes , one altered copy of the gene usually leads to less severe health problems than those in affected males, or it may cause no signs or symptoms at all.
A condition is considered Y-linked if the altered gene that causes the disorder is located on the Y chromosome , one of the two sex chromosomes in each of a male's cells. Because only males have a Y chromosome, in Y-linked inheritance, a variant can only be passed from father to son. Y chromosome infertility , some cases of Swyer syndrome. 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 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 variants to their children. Conditions resulting from variants 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. Dominant inheritance means an abnormal gene from one parent can cause disease.
This happens even when the matching gene from the other parent is normal. The abnormal gene dominates. This disease can also occur as a new condition in a child when neither parent has the abnormal gene. This is true for each pregnancy.
It means that each child's risk for the disease does not depend on whether their sibling has the disease. If someone is diagnosed with an autosomal dominant disease, their parents should also be tested for the abnormal gene. Examples of autosomal dominant disorders include Marfan syndrome and neurofibromatosis type 1. Patterns of single-gene inheritance. Philadelphia, PA: Elsevier; chap 7.
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