Final answer:
A mutation changing UAA to UAC would change a stop codon into a tyrosine codon, resulting in a nonsense mutation that could lead to a truncated, nonfunctional protein.
Step-by-step explanation:
If there were a mutation that caused a codon to change from UAA to UAC, we would expect the nature of the codon's function to significantly change. The UAA codon is a stop codon, which signals the end of translation and the release of the newly synthesized protein. However, UAC codes for the amino acid tyrosine. This type of mutation is called a nonsense mutation because it converts a sense codon into a stop codon, leading to premature termination of the protein. If the mutation occurs early in the gene, the resulting protein would likely be truncated and nonfunctional.