Which of the following mutations is most likely to have a dramatic effect on the sequence of a protein?

A deletion mutation involves the removal of one or more nucleotides from a DNA sequence. This can have a profound impact on the resulting protein because it alters the reading frame of the genetic code, which changes how codons are read during translation. If a deletion occurs not in multiples of three, it causes a frameshift mutation. This shift can result in a completely different sequence of amino acids down the line, potentially leading to a dysfunctional protein or an entirely different protein altogether.

In contrast, substitution mutations might only change one amino acid or possibly none at all (as in silent mutations), and point mutations tend to have a less drastic effect compared to deletions, especially if they do not cause a frameshift. Silent mutations specifically do not alter the amino acid sequence of the protein. Thus, deletions are indeed the type of mutation that are most likely to create significant changes in protein structure and function.