What type of mutation does not change the primary amino acid sequence of a protein?

A silent mutation is a specific type of mutation that does not alter the primary amino acid sequence of a protein. This type of mutation occurs when a change in the nucleotide sequence of DNA does not result in a change in the amino acid that is incorporated into the protein during translation. This can happen due to the redundant nature of the genetic code, where multiple codons can encode the same amino acid.

For example, if a codon is changed from UUC to UUU, both codons encode for the amino acid phenylalanine, thus the overall protein remains unchanged despite the alteration at the nucleotide level. This feature of silent mutations is critical in understanding how genetic variations can occur without affecting the final protein product, which is significant for evolutionary processes and genetic diversity.

In contrast, missense mutations lead to a different amino acid being incorporated into the protein, nonsense mutations result in a premature stop codon, and frameshift mutations alter the reading frame of the codons, both of which would ultimately change the resultant protein's amino acid sequence. Hence, silent mutations stand out for preserving the integrity of the protein structure despite changes at the DNA level.