Final answer:
A DNA mutation can result in an altered protein that may lead to a new phenotype if the protein's function is significantly changed. The phenotypic outcome depends on the role and functionality of the altered protein.
Step-by-step explanation:
A mutation in the DNA sequence can lead to the production of a protein created with an altered amino acid sequence, potentially causing changes in the structure and function of the protein. The effect of a mutated protein on a phenotype depends on the significance of the change to the protein's function. If the protein functions differently, it can result in a new phenotype. If the function is not significantly affected, then the phenotype might remain unchanged. However, if the protein is crucial and the mutation causes it to malfunction or not be produced at all, this could prevent the expression of the phenotype or result in a detrimental effect on the organism.
Considering the given options:
A) The phenotype would not be expressed.
B) The phenotype would be unchanged.
C) A new phenotype would appear.
D) Both phenotypes (original and mutated) would be expressed.
Without additional context, the most accurate answer could be C) A new phenotype would appear, if the mutation notably changes the protein's function.