Final answer:
A carrier is a person who is heterozygous for a recessive gene and can pass on a genetic disorder without having symptoms themselves. This is important in autosomal recessive disorders like cystic fibrosis and sickle cell anemia. Carrier diagnosis helps in knowing the likelihood of transmitting these disorders.
Step-by-step explanation:
A carrier is a heterozygous individual who does not display symptoms of a recessive genetic disorder but can transmit the disorder to their offspring. When a genetic disorder is inherited in an autosomal recessive pattern, carriers are essential for its transmission. For example, in the case of cystic fibrosis, a disease caused by a recessive allele, a person must inherit two copies of the defective gene in order to express the disease phenotype. The heterozygous parents do not show any symptoms themselves because their unaffected allele compensates for the defective one. However, if both parents are carriers, there is a 25% chance that their child will inherit the disorder. In some cases, being a carrier can confer an advantage, such as in sickle cell anemia, where carriers can have resistance to malaria infection. Nonetheless, carrier diagnosis is important for many hereditary diseases, including cystic fibrosis, Tay-Sachs disease, and others, enabling individuals to be aware of their carrier status.