Slide show: How genetic disorders are inherited
Illustration of autosomal recessive inheritance pattern
Previous Next 4 of 6 Autosomal recessive inheritance pattern

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 parents must be carriers. The child inherits two copies of the mutated gene — one from each parent.

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) with every pregnancy.

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