Title: 
Headings: 

Content: Single-gene diseases are usually inherited in one of several patterns depending on the
location of the gene and whether one or two normal copies of the gene are needed for the
disease phenotype to manifest. The expression of the mutated allele with respect to the normal allele can be characterized
as dominant, co-dominant, or recessive. There are five basic modes of inheritance for
single-gene diseases: autosomal dominant, autosomal recessive, X-linked dominant, X-linked
recessive, and mitochondrial. Genetic heterogeneity is a common phenomenon with both single-gene diseases and complex
multi-factorial diseases. It should not be surprising that multiple affected family members
may experience different levels of disease severity and outcomes. This effect may be due to
other genes influencing the disease phenotype or different mutations in the same gene
resulting in similar, but not identical phenotypes. Some excellent resources for information
about single-gene diseases is the Online Mendelian Inheritance in Man (OMIM; http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=OMIM) and
GeneTests/GeneClinics (http://www.genetests.org). Patterns of Inheritance
Autosomal Dominant
Each affected person has an affected parent
Occurs in every generation
Autosomal Recessive
Both parents of an affected person are carriers
Not typically seen in every generation
X-linked Dominant
Females more frequently affected
Can have affected males and females in same generation
X-linked Recessive
Males more frequently affected
Affected males often present in each generation
Mitochondrial
Can affect both males and females, but only passed on by females
Can appear in every generation
View in own window
Inheritance Pattern
Disease Examples
Autosomal Dominant
Huntington’s disease,
neurofibromatosis, achondroplasia, familial hypercholesterolemia
Autosomal Recessive
Tay-sachs disease, sickle cell anemia, cystic
fibrosis, phenylketonuria (PKU)
X-linked Dominant
Hypophatemic rickets (vitamin D-resistant
rickets), ornithine transcarbamylase deficiency
X-linked Recessive
Hemophilia A, Duchenne muscular dystrophy
Mitochondrial
Leber’s hereditary optic neuropathy,
Kearns-Sayre syndrome
Copyright© 2008, Genetic Alliance.