Question

Cathy is pregnant for the second time. Her first child Donald, has Cystic fibrosis (CF). Cathy has two brothers Charles and Colin and a sister Cindy. Charles is married to an unrelated woman, Carolyn, and has a 2-year- old daughter, Debbie. Cathy’s parents are Bob and Betty. Betty’s sister Barbara is the mother of Cathy’s husband, Calvin. There is no previous family history of Cystic fibrosis.

What is the pattern of transmission of Cystic Fibrosis? What is the risk for Cystic Fibrosis for Cathy’s next child? Which people in this pedigree are obligate heterozygotes?

Answer 1

1)Cystic fibrosis is inherited in an autosomal recessive manner.

2)one-fourth(1/4) is the risk for the cystic fibrosis for Cathy's next child.

3)Calvin and Cathy are obligatory heterozygotes.

Given that Calvin and Cathy are first cousins,it is also very likely that they inherited their mutant allele through Betty and Barbara from the same grandparent.Thus , Betty and Barbara are very likely to be carriers but it is not obligatory.It is theoretically possible that Cathy inherited her CF allele from Bob and that Calvin inherited his from his father, Barbara's husband.