Questions: This test: 66 point(s) Question 21 of 66 possible This question: 1 point(s) possible Submit test Part A Select the correct explanation for the fact that a carrier of a recessive genetic disorder does not have the disorder. In a recessive disorder, only a single functioning allele is necessary to determine a normal phenotype. The dominant allele for the gene determining the disorder represses protein production from the recessive allele. Affected individuals have recessive mutations, but a carrier has a dominant mutation. Next

The answer is the first one: In a recessive disorder, only a single functioning allele is necessary to determine a normal phenotype.

Explanation for each option:

1. In a recessive disorder, only a single functioning allele is necessary to determine a normal phenotype.

   • This is correct. In recessive genetic disorders, an individual must inherit two copies of the recessive allele (one from each parent) to express the disorder. A carrier has one normal (dominant) allele and one recessive allele, and the presence of the dominant allele is sufficient to produce a normal phenotype, preventing the disorder from manifesting.

2. The dominant allele for the gene determining the disorder represses protein production from the recessive allele.

   • This is incorrect. In most cases, the dominant allele does not actively repress the recessive allele. Instead, the dominant allele typically produces a functional protein that compensates for the lack of function from the recessive allele.

3. Affected individuals have recessive mutations, but a carrier has a dominant mutation.

   • This is incorrect. Carriers do not have a "dominant mutation." They have one normal (dominant) allele and one recessive allele. The term "mutation" is not typically used to describe the normal allele in carriers.

In summary, carriers of a recessive genetic disorder do not exhibit the disorder because they have one normal allele that is sufficient to produce a normal phenotype.