A mutation occurs in a portion of DNA and does not change the amino acid sequence of a protein
This type of mutation is called a silent mutation. In a silent mutation, a change occurs in the DNA sequence, but it does not result in a change in the corresponding amino acid sequence of the protein.
Silent mutations can occur due to the degeneracy of the genetic code. The genetic code is organized in such a way that multiple codons (sequences of three nucleotides) can code for the same amino acid. For example, the codons GGC, GGA, GGG, and GGU all code for the amino acid glycine.
If a mutation occurs in the third nucleotide of a codon, it may still code for the same amino acid due to this degeneracy. For instance, if the original codon is GGC (coding for glycine) and a mutation changes it to GGU, the third nucleotide change from C to U does not alter the coding for glycine, so the resulting amino acid sequence of the protein remains unchanged.
Silent mutations can have no effect on the phenotype of an organism because they do not cause any changes in the protein product. However, they can still play a role in evolution as they can accumulate over time and contribute to genetic diversity.