Concept:Nonsense codons, also known as stop codons, signal termination of protein translation and do not code for any amino acid.
Explanation:The genetic code has three stop codons: UAA, UAG, and UGA.
Option A: AUG is the start codon that codes for methionine — it is a sense codon, not a nonsense codon.
Option B: UAA is a stop codon — therefore it is a nonsense codon.
Option C: UUU codes for phenylalanine — it is a sense codon.
Option D: UGC codes for cysteine — it is also a sense codon.
Only UAA, UAG, and UGA are nonsense codons. Among the given choices, only UAA fits.
Answer:Option B (UAA) is the correct answer.