## **Core Concept**
The question tests understanding of molecular biology, specifically the genetic code and the concept of stop or termination codons, also known as non-sense codons when they signal termination rather than code for an amino acid.

## **Why the Correct Answer is Right**
The correct answer, UGA, is one of the three stop codons in the genetic code. These codons signal the termination of protein synthesis. The three stop codons are UAA, UAG, and UGA. They do not code for any amino acid but instead signal the end of the translation process.

## **Why Each Wrong Option is Incorrect**
- **Option A:** AUG is a start codon, coding for methionine in eukaryotes and formylmethionine in prokaryotes. It signals the initiation of protein synthesis, not termination.
- **Option B:** UAA is indeed a stop codon, similar to UGA and UAG. However, the question seeks a singular non-sense codon, and UAA is another correct example but not the one chosen as the correct answer.
- **Option D:** UAG is also a stop codon. Like UAA and UGA, it signals the termination of protein synthesis.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that mutations leading to the formation of a premature stop codon (like UAA, UAG, or UGA in a coding sequence) can lead to a truncated, often nonfunctional protein. This is a critical concept in understanding genetic diseases.

## **Correct Answer:** . UGA