Dennis 25 and Lucy 22 which pre-pregnancy genetic counseling. Dennis had two normal brothers and a normal sister, but also had a brother and a sister who dies 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. Both Dennis and Lucy are Caucasian and are non-consanguineous.
A. Draw a pedigree based on the information you have. Indicate proband and affected individuals, and provide a key.
B. Based on pedigree analysis, what is the most likely mode of inheritance of cystic fibrosis in this family?
Why?
C. Assuming the inheritance mode in B, what is the chance that Dennis is heterozygous for the cystic fibrosis gene?
D. The incidence of cystic fibrosis in the Caucasian population is about 1/2000, and the heterozy gote frequency about 1/25. Assuming Dennis and Lucy are not consanguineous, calculate the risk that Dennis and Lucy's first child is affected, what is the chance that their second child will also be affected?
E. Assuming Lucy was also heterozygous and that prenatal diagnosis of cystic fibrosis is not available for this family, what are Lucy and Dennis' options for decreasing their risk of having an affected child?