Carriers of cystic fibrosis have some protection against intestinal infections such as cholera.However,people with two copies of the cystic fibrosis allele develop a life-threatening disease.The mutant allele is very common in people of northern European descent because of

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Heterozygote advantage explains why the cystic fibrosis allele persists in the population, especially among people of northern European descent. Carriers of one copy of the allele (heterozygotes) have some protection against certain intestinal infections, which can confer a survival advantage in environments where such diseases are prevalent. This advantage does not extend to individuals with two copies of the allele, who suffer from the severe symptoms of cystic fibrosis.

Carriers of Cystic Fibrosis Have Some Protection Against Intestinal Infections