Question 5 • IS - O - 3490 - The Living Earth B CP Online
Cystic fibrosis is a genetic disorder. It is a recessive trait that is determined by two alleles. Suppose two parents each carry at least one recessive allele, but neither of them has cystic fibrosis. Which statement reflects the likelihood of a child of these parents having cystic fibrosis?
Answer
A
The child cannot have the disease because only the dominant alleles will be passed on.
B
The child will have the disease because only recessive alleles will be passed on.
C
The child may or may not have the disease because a recessive gene from each parent may be passed on.
D
The child may or may not have the disease because the disease does not depend on the alleles of the parents.
Explanation
Because cystic fibrosis is recessive and neither parent has the disease, each parent can be a carrier with one dominant allele and one recessive allele. A child will have cystic fibrosis only if the recessive allele is passed on by both parents; otherwise, the child will not have the disease. So the child may or may not have cystic fibrosis, as stated in choice C.
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