In an example of a silent mutation, if the codon changes from ACU to ACA, what can be inferred?

In the case of a silent mutation, the alteration of the codon from ACU to ACA results in the same amino acid being produced. Both codons encode for the amino acid threonine. This phenomenon occurs due to the redundancy of the genetic code, where multiple codons can specify the same amino acid. Silent mutations typically do not result in any effect on the protein's function because the sequence and structure of the resulting polypeptide remain unchanged, highlighting the resilience of the genetic code against certain types of mutations.

The other choices involve changes that do not apply in this scenario, such as a change in the specified amino acid or the introduction of a stop codon, which would signify a more impactful mutation. Additionally, frameshift mutations involve insertions or deletions of nucleotides, altering the reading frame and likely changing the resulting amino acids. However, since the shift from ACU to ACA does not change the amino acid produced, it demonstrates the concept of silent mutation effectively.