* Original Codon: UAG

* Mutation: UAG to UCG

* Original Amino Acid: UAG is a stop codon, meaning it signals the end of protein synthesis.

* New Codon: UCG

* New Amino Acid: UCG codes for Serine (Ser).

Therefore, the mutation would change a stop codon to a codon that codes for the amino acid Serine.

This type of mutation is known as a nonsense mutation because it changes a codon that normally specifies an amino acid into a stop codon, resulting in a truncated protein. In this case, however, it actually changes a stop codon into a sense codon, resulting in an extended protein.