Final answer:
Cystic fibrosis is caused by a mutated CFTR gene, leading to a non-functional protein that results in thick mucus build-up, especially in the lungs. It is an autosomal recessive disorder prevalent in Northern European populations.
Step-by-step explanation:
Cystic fibrosis is caused by a recessive loss-of-function mutation that encodes a protein called the cystic fibrosis transmembrane conductance regulator, or CFTR. The CFTR protein is an integral membrane protein that is crucial for transporting Cl− ions out of cells. In individuals with cystic fibrosis, the gene for CFTR is mutated, resulting in a defective channel protein that is typically degraded by the cell rather than being incorporated into the membrane. This defective protein leads to the production of thick and sticky mucus that clogs various organs, most notably the lungs, causing severe respiratory issues and other complications.
Furthermore, cystic fibrosis is an autosomal recessive genetic disease, where an individual must inherit two copies of the faulty gene to manifest the disease. Carriers of one mutant gene have sufficient functioning CFTR proteins to avoid symptoms. The disease is more prevalent in people of Northern European ancestry, and despite its severe consequences, has persisted possibly due to a heterozygote advantage where carriers may resist certain infectious diseases better.