Autosomal recessive inheritance

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Each gene has two copies

Traits (such as eye color or risk for disease) are passed to your children by genes. Each person has two genes for each trait. One gene is from the mother and one gene is from the father.

Autosomal recessive inheritance refers to conditions caused by changes (“mutations”) in genes located on one of the 22 pairs of autosomes. Autosomes are the numbered chromosomes that are the same in all males and females. Autosomal conditions occur in both men and women and are not related to whether a person is male or female.

Autosomal Recessive Inheritance

“Affected” people inherit two changed copies

In an autosomal recessive disorder, two changed copies of a gene are inherited—one from each of the parents—which causes the child to have the disorder. The child is called “affected” because she or he has the disorder.

“Carriers” inherit only one changed copy

A carrier has only one changed copy of the gene. They are called “carriers” of the trait because they do not show any signs of the disorder. Although they have one copy of a gene that is changed, the partner copy of the gene is working correctly, so they do not develop the disorder.

Who is “affected”

When both parents are carriers for a recessive disorder, each child has a 1 in 4 (25 percent) chance of inheriting the two changed gene copies. A child who inherits two changed gene copies will be “affected,” meaning the child has the disorder.

There is a 1 in 2 (50 percent) chance that the child will inherit one changed copy and one normal copy of the gene, and therefore be an unaffected carrier (just like the parent).

There is a 1 in 4 (25 percent) chance that the child will inherit both normal copies of a gene, and be unaffected and not a carrier.

If only one parent is a carrier and the other is not, none of the children will have the condition. But each child will have a 50 percent chance of being a carrier.

Example: cystic fibrosis

For example, cystic fibrosis (CF) is an autosomal recessive disease caused by mutations in a gene called CFTR. If both parents are carriers, each parent can pass on the changed copy or the normal copy to their children. Children who inherit two changed copies of the CFTR gene are “affected” and have the disease cystic fibrosis.

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