Hi Nicole,

The way I understood it, when you add a nucleotide into the open reading frame (ORF), it will cause a frameshift mutation downstream to where the nucleotide was added. So the amino-terminal sequence (at the start) wouldn't be changed, but the carboxy-terminal (near the end) more probably will. The stop codon comes after the ORF, which was unchanged as the question said, so its probably something before it (carboxy end).

Hope this helps!