3. Dennis 25 and Lucy 22 are at pre-pregnancy genetic counselling clinic. Dennis had two
normal brothers and a normal sister, but also had a brother and a sister who died at 22 and 18
years, respectively, of cystic fibrosis (a condition of malabsorption do to pancreatic insufficiency
and recurrent pulmonary infection with progressive respiratory insufficiency, usually leading to
death in early adulthood). Dennis is in good health, as is Lucy. Dennis' parents are alive and well
in their late 50's and none of their other relatives have died young or had similar problems.
A. Draw a pedigree based on the information you have. Indicate normal and affected individuals,
and provide a key. (8 marks)
B. What are the genotypes of the Denis, his parents, and his sibling? (8 marks)
C. Assuming the inheritance mode in B, what is the chance that Dennis is heterozygous for the
cystic fibrosis gene? (2 marks)