Slide show: How genetic disorders are inherited
Illustration of autosomal recessive inheritance pattern
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In an autosomal recessive disorder, the mutated recessive gene is located on one of the nonsex chromosomes (autosomes). To inherit an autosomal recessive disorder — such as cystic fibrosis, sickle cell anemia or phenylketonuria (PKU) — both copies of the gene must be mutated.

A "carrier" is an unaffected individual who has one copy of the mutated gene and the other copy is normal. Two carriers have a 25 percent chance of having an unaffected child with two normal copies of a gene (left), a 50 percent chance of having an unaffected child who also is a carrier (middle), and a 25 percent chance of having an affected child with two mutations (right).

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