Carrier Status Explained

Carrier is the term used in genetic counseling to designate an individual with a genetic mutation associated with a disease that may or may not display disease symptoms.

Carriers are associated with diseases inherited as recessive traits. In order to have the disease, the individual must have inherited the mutated alleles from both parents.

For recessive disorders, an individual having one normal allele and one mutated allele does not have the disease. Two carriers may produce a child with the disorder.

Gene Frequency and Carrier Frequency

The mutant alleles responsible for a recessive disorder are generally rare, and so most people will not have even copy of the mutant allele. Among individuals with at least one copy of the mutant allele, however, the frequency of clinically affected heterozygotes with one normal allele and one mutant allele is always much greater than the frequency of affected individuals with two rare mutant alleles.

Because an autosomal recessive disorder must be inherited through both parents, the risk that any carrier will have an affected child depends on the chance that his or her mate is also a carrier of a mutant allele for the condition. Thus, knowledge of the carrier frequency of a disease is clinically important for genetic counseling.

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    Adapted from Thompson & Thompson Genetics in Medicine E-Book By Robert L. Nussbaum, Roderick R. McInnes, Huntington F Willard