Merck Manual

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When a Parent Has an Abnormal Gene

When a Parent Has an Abnormal Gene

Inheritance Pattern

Chance of Inheriting the Disorder

Chance of Being a Carrier*

Autosomal dominant

50% for sons and daughters

0%

Autosomal recessive

25% for sons and daughters if both parents are carriers*

67% for children with no symptoms of the disorder if both parents are carriers

50% if only one parent has the gene

X-linked dominant

50% when the mother has the gene, usually only in daughters because the abnormal gene is often lethal in sons

0%

X-linked recessive

50% for sons when the mother has the gene

50% for daughters when the mother has the gene

100% for daughters when the father has the gene

* Carriers have only one abnormal gene and usually have no symptoms of the disorder that the gene causes.