The family tree below shows the inheritance of the genetic condition cystic fibrosis (CF). Cystic fibrosis is caused by a faulty version of a gene that controls they type of mucus present in body structures like the lungs and the gut. People with cystic fibrosis produce a very sticky form of mucus and may have difficulty breathing. Which version of the gene masks the effect of the other version?
![A family tree that shows how people become infected with cystic fibrosis. The mother has the version of the gene that does not cause CF, the father has the version of the gene that does cause CF. Both children have a combination of both, and therefore carry but do not have CF.]()