What might cause a mutation to have no observable effect on the resulting protein?

The correct choice is based on the concept of redundancy in the genetic code, also known as codon redundancy or degeneracy. The genetic code consists of 64 different codons, which are sequences of three nucleotides that correspond to specific amino acids. However, there are only 20 amino acids that proteins are built from. This means that most amino acids are encoded by more than one codon, so a change in the DNA sequence (a mutation) can sometimes result in the same amino acid being incorporated into a protein.

For example, if a mutation changes one codon to another that codes for the same amino acid, the overall structure and function of the protein may remain unchanged. Thus, the mutation could have no observable effect despite occurring in a coding region. This is an essential aspect of how genetic variations can arise without impacting the phenotype.

In contrast, mutations occurring in non-coding regions or those leading to significant changes in the protein structure typically will have observable effects. Redundancy allows for some mutations to be effectively 'silent' with no impact on the protein's functionality, which is why recognizing this concept is crucial in understanding genetic mutations.