Handbook

What are the different ways in which a genetic condition can be inherited?

Some genetic conditions are caused by mutations in a single gene. These conditions are usually inherited in one of several straightforward patterns, depending on the gene involved:

Inheritance pattern	Description	Examples
Autosomal dominant	Only one mutated copy of the gene is needed for a person to be affected by an autosomal dominant disorder. Each affected person usually has one affected parent (illustration).	Huntington disease, neurofibromatosis 1
Autosomal recessive	Two copies of the gene must be mutated for a person to be affected by an autosomal recessive disorder. An affected person usually has unaffected parents who each carry a single copy of the mutated gene (and are referred to as carriers) (illustration).	cystic fibrosis, sickle cell anemia
X-linked dominant	X-linked dominant disorders are caused by mutations in genes on the X chromosome. Only a few disorders have this inheritance pattern. Females are more frequently affected than males, and the chance of passing on an X-linked dominant disorder differs between men (illustration) and women (illustration).	X-linked hypophosphatemia
X-linked recessive	X-linked recessive disorders are also caused by mutations in genes on the X chromosome. Males are more frequently affected than females, and the chance of passing on the disorder differs between men (illustration) and women (illustration).	hemophilia A, Duchenne muscular dystrophy
Mitochondrial	This type of 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 conditions to their children (illustration).	Leber's hereditary optic neuropathy (LHON)

Many other disorders are caused by a combination of the effects of multiple genes or by interactions between genes and the environment. Such disorders are more difficult to analyze because their genetic causes are often unclear, and they do not follow the patterns of inheritance described above. Examples of conditions caused by multiple genes or gene/environment interactions include heart disease, diabetes, schizophrenia, and certain types of cancer. For more information, please see What are complex or multifactorial disorders?.

Disorders caused by changes in the number or structure of chromosomes 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 can also influence how a disorder is inherited: What are genomic imprinting and uniparental disomy?

For more information about inheritance patterns:

The Genetics and Public Policy Center provides an introduction to hereditary mutations This link leads to a site outside Genetics Home Reference. , including their patterns of inheritance.

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