Which type of mutation is least likely to change the outcome of a protein?

A silent mutation is least likely to change the outcome of a protein because it leads to a change in the nucleotide sequence of a gene that does not alter the amino acid sequence of the resulting polypeptide. This usually occurs due to the redundancy in the genetic code, where multiple codons can encode the same amino acid. For example, if a silent mutation changes a codon from GAA to GAG, both codons still specify the amino acid glutamic acid, thus leaving the protein unchanged.

In contrast, missense mutations result in the substitution of one amino acid for another, which can affect the structure and function of the protein, potentially leading to altered biological activity. Nonsense mutations create a premature stop codon, leading to truncated proteins that are often nonfunctional. Frameshift mutations, caused by insertions or deletions of nucleotides that are not in multiples of three, can drastically change the entire downstream amino acid sequence, often resulting in a completely dysfunctional protein.

Hence, the silent mutation stands out as the type that has the least impact on the protein's final structure and function, maintaining its intended biological role.