Biology worksheet focusing on DNA mutations and protein coding, designed for educational purposes.

Final Answer:
Substitution

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Explanation:
The question asks: *A geneticist found that a specific mutation had no effect on the protein coded for by a gene. What is the most likely type of mutation?*

Let’s think step by step:
- A mutation changes the DNA sequence.
- That change affects mRNA, which then affects the protein made during translation.
- But here, the protein did not change at all — it’s the same as before the mutation.

Now look at the table in the task:
- Substitution: one DNA base is swapped for another. Sometimes, this still gives the *same amino acid* because the genetic code is “redundant” (multiple codons can code for the same amino acid). This is called a *silent mutation*.
- Insertion or Deletion: these shift the whole reading frame (unless it’s exactly 3 bases), so almost always change many amino acids — the protein *will* be different.
- Premature stop signal also changes the protein drastically.

So if the protein is unchanged, the only likely option is a substitution that didn’t change the amino acid — a silent substitution.

That’s why the answer is: Substitution.