Nancy and Cliff had four children who did not have cystic fibrosis, but their fifth child was born with the disease. Cystic fibrosis is carried on a recessive gene. Given what you've learned in this chapter, how could this happen?
A) It wasn't until the fifth child that both parents passed on the allele for this illness.
B) Recessive genes normally skip a generation, but after the parents had five children, the gene was expressed.
C) Their fifth child must have been a boy, which makes it more probable that he would have the illness.
D) Their fifth child must have been a girl, which makes it more probable that she would have the illness.

Question

Quizplus · Accepted Answer

In order for a child to inherit a recessive genetic disorder like cystic fibrosis, both parents must carry a copy of the mutated gene. If the parents are carriers, each of their children has a 25% chance of inheriting two copies of the mutated gene and thus having the disorder. It is possible for multiple children in a family to not have the disorder if they inherit the normal gene from both parents, but for the fifth child to have the disorder, both parents must have passed on the recessive gene to that child.

Nancy and Cliff Had Four Children Who Did Not Have