Problem
Sheala and Zoltan are thinking of having a child together, but they are worried. Both of them have siblings who died in their teens from a disease called cystic fibrosis, which is an autosomal (non-sex-linked) recessive disorder. Sheala also had a cousin who died at age 10 from Duchenne muscular dystrophy (DMD), a recessive X-linked disease. On top of all of this, both Sheala and Zoltan have thalassemia minor. Given this unfortunate genetic background, both prospective parents go for genetic testing, the results of which indicate that both are carriers for cystic fibrosis. In addition, Sheala is a carrier for DMD.
A. What is the probability that a child born to Sheala and Zoltan would have thalassemia major, but neither of the other diseases, assuming you knew that the child was male?
B. What is the probability that a child in this mating would have DMD and cystic fibrosis, but not thalessemia major, assuming you knew that the child was female?
C. What is the probability that a child born to Sheala and Zoltan would have at least one of the three diseases--cystic fibrosis, DMD or thalassemia major--assuming you don't know the sex of the child?