Answer:
G
Explanation:
your have to look at the second triplet of bases: AGT since it says the chain is only 2 amino acids long (so the 3rd triplet must be the stop codon).
Now remember that for the DNA-mRNA transcription A becomes U, T becomes A, C becomes G and vice versa. So to codify a UGA codon you need ACT in the DNA. Since we have AGT instead, it means the G was changed by the mutation.
