What about parents with cystic fibrosis?
Interestingly, a person with cystic fibrosis can also have children without the disease. How does this work? It can only work if the other parent is healthy and can pass on a healthy gene. That way, the healthy gene will override the inherited chloride channel mutation. However, all children of a person with cystic fibrosis will at least by a carrier for the bad allele. That's because a person with cystic fibrosis only has mutated alleles to give.