Understanding Silent Mutations in Genetics

A point mutation refers to a change in a single nucleotide base within the DNA sequence. These mutations can have various effects on the resulting protein, depending on how they alter the genetic code.

Types of Point Mutations

Let's examine the different types of mutations mentioned in the options to understand which one fits the description:

• Missense Mutation: This type of point mutation results in a codon that codes for a different amino acid than the original codon. This change alters the protein's structure or function.
• Nonsense Mutation: This point mutation changes a codon that normally codes for an amino acid into a premature stop codon. This leads to the termination of protein synthesis, resulting in a truncated and usually non-functional protein.
• Silent Mutation: This is a point mutation where a change in the DNA sequence results in a codon that codes for the exact same amino acid. This phenomenon occurs because the genetic code is degenerate, meaning that multiple different codons can specify the same amino acid. For instance, the amino acid Alanine can be coded by the codons $GCT$, $GCC$, $GCA$, or $GCG$. A mutation changing $GCT$ to $GCC$ would be a silent mutation because both codons still result in Alanine being incorporated into the protein.
• Frameshift Mutation: This type of mutation is typically caused by the insertion or deletion of nucleotides in a number not divisible by three. This shifts the reading frame of the codons during translation, altering every amino acid coded downstream from the mutation site and often leading to a premature stop codon. While a point mutation is a change in a single base, frameshifts usually involve more than one base change (insertion/deletion).

Identifying the Correct Mutation Type

The question specifically asks for a point mutation that changes a codon but does not alter the resulting amino acid. Based on the definitions above, this description precisely matches a silent mutation due to the degeneracy of the genetic code.