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→Classification of congenital disorders:
!Pattern of inheritance !! Description !! Example
!Pattern of inheritance !! Description !! Example
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|X-linked dominant || •By mutations in genes on the X chromosome,
|X-linked dominant || *By mutations in genes on the X chromosome,
* In females, a mutation in one of the two copies of the gene in each cell is sufficient to cause the disorder.
* In males, 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. || fragile X syndrome
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|X-linked recessive || • Caused by mutations in genes on the X chromosome.
|X-linked recessive ||* Caused by mutations in genes on the X chromosome.
* A mutation would have to occur in both copies of the gene to cause the disorder in females.
* In males, one altered copy of the gene in each cell is sufficient to cause the condition.
* Males are affected by X-linked recessive disorders much more frequently than females.
|| hemophilia, Fabry disease
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| Y-linked || • Caused by mutations in genes on the Y chromosome.
| Y-linked || * Caused by mutations in genes on the Y chromosome.
* So, the mutation can only be passed from father to son.
|| Y chromosome infertility, some cases of Swyer syndrome
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|Autosomal dominant || • One mutated copy of the gene in each cell is sufficient for a person to be affected.
|Autosomal dominant || * One mutated copy of the gene in each cell is sufficient for a person to be affected.
* An affected person can inherit the condition from an affected parent.
* the condition may result from a new mutation in the gene (e, without any family history)
|| Huntington disease, Marfan syndrome
|| Huntington disease, Marfan syndrome
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|Autosomal recessive || • Both copies of the gene in each cell should have mutations.
|Autosomal recessive || * Both copies of the gene in each cell should have mutations.
* Typically not seen in every generation of an affected family.
|| cystic fibrosis, sickle cell disease
|| cystic fibrosis, sickle cell disease
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|Codominant || • Two different versions (alleles) of a gene are expressed.
|Codominant || * Two different versions (alleles) of a gene are expressed.
* Both alleles influence the genetic trait or determine the characteristics of the genetic condition.
|| ABO blood group, alpha-1 antitrypsin deficiency
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| Mitochondrial || • Also known as maternal inheritance
| Mitochondrial || * Also known as maternal inheritance
* Applies to the genes in mitochondrial DNA
* Only females can pass on mitochondrial mutations to their children as only egg cells contribute mitochondria to the developing embryo.
||Leber hereditary optic neuropathy (LHON)
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