Final answer:
Carriers of cystic fibrosis are relatively resistant to tuberculosis due to balanced polymorphism, which gives carriers an advantage against tuberculosis bacteria.
Step-by-step explanation:
Carriers of cystic fibrosis are relatively resistant to tuberculosis. This is likely due to a phenomenon known as balanced polymorphism, where genetic diversity, such as being a carrier of an autosomal recessive disease, can confer an advantage in certain environmental contexts or against specific threats. In the case of cystic fibrosis, carriers produce enough normal CFTR protein to avoid the disease, but the slight abnormality in chloride ion transport may provide a less hospitable environment for tuberculosis bacteria.
Cystic fibrosis is caused by a mutation in the CFTR gene, which leads to thick, sticky mucus in various organs such as the lungs and intestines. This thick mucus can block airways and lead to infections; however, it may also create an inhospitable environment for the tuberculosis bacteria. As a result, carriers who have one normal and one mutated CFTR gene may experience a protective benefit against tuberculosis infection.