Question

a person inherits a functional cystic fibrosis allele from both parents. what phenotype will this person have?
the person will be healthy, but will pass the cystic fibrosis genes to all of his or her offspring.
the person will have a normal phenotype, but will be a genetic carrier of cystic fibrosis.
the person will have cystic fibrosis.
the person will have a normal genotype and be healthy.

Explanation:

Cystic fibrosis is an autosomal recessive disorder. Let the normal allele be \(A\) and the mutant allele be \(a\). A person with two functional alleles (genotype \(AA\)) has a normal genotype. Since having two normal alleles means there is no mutant allele to cause the disease - causing phenotype, the person will be healthy.

• The first option is wrong because if a person has two functional alleles (\(AA\)), they do not carry the disease - causing allele (\(a\)) to pass on to offspring.
• The second option is incorrect. A genetic carrier has a genotype like \(Aa\) (one normal and one mutant allele), but here the genotype is \(AA\).
• The third option is wrong as the presence of two mutant alleles (\(aa\)) is required for a person to have cystic fibrosis.

Answer:

The person will have a normal genotype and be healthy.