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 may or may not have the disease because the disease does not depend on the alleles of the parents.
B
The child may or may not have the disease because a recessive gene from each parent may be passed on.
C
The child will have the disease because only recessive alleles will be passed on.
D
The child cannot have the disease because only the dominant alleles will be passed on.
Explanation
A person with a recessive genetic disorder has two recessive alleles. Since neither parent has cystic fibrosis but each carries a recessive allele, each parent must also have a dominant allele. A child may inherit the recessive allele from both parents and have cystic fibrosis, or inherit at least one dominant allele and not have it. Therefore, the child may or may not have the disease because a recessive gene from each parent may be passed on.
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