1. cystic fibrosis: suppose a couple has come to see you to discuss the probability of their children having cystic fibrosis (cf). cf is known to be an autosomal recessive disease caused by a single gene mutation that has pleiotropic effects including thick mucus in the lungs and excessively salty sweat. after discussions with the couple, you learn that they both have a history of the disease in their families. both the man and his wife are phenotypically normal, but both have one parent and one sibling with cf. the other parent in each case is phenotypically normal. explain to the couple the probability of their children having cf or being carriers for the cf gene. explain to them why their children can have the disease even though neither of them have the disease. draw a punnett square to illustrate your points.