Cystic fibrosis is caused by a recessive gene. If c = normal and C = cystic fibrosis, how can a child with cystic fibrosis have two parents who do not have cystic fibrosis?
a) Both parents must be carriers of the cystic fibrosis gene
b) One parent must be a carrier of the cystic fibrosis gene
c) Both parents must have cystic fibrosis
d) It is not possible for a child to have cystic fibrosis if both parents do not have it