Degeneracy of the genetic code: Which codon pair best illustrates that different codons can specify the same amino acid (i.e., degeneracy)?

Introduction / Context:
The genetic code is degenerate, meaning most amino acids are encoded by more than one codon. Recognizing synonymous codons is crucial for translation, codon optimization, and understanding mutations.

Given Data / Assumptions:

• Standard genetic code (not mitochondrial variants).
• We seek pairs that encode the same amino acid.
• Stop codons and start codon roles are considered.

Concept / Approach:
CAU and CAC both encode histidine, demonstrating degeneracy. By contrast, UAA is a stop codon and UAC encodes tyrosine; AUG encodes methionine (start) while AUA encodes isoleucine; UUA encodes leucine while UUC encodes phenylalanine.

Step-by-Step Solution:
Check each pair against the codon table.Identify synonymous pair: CAU ↔ CAC → histidine.Therefore, select CAU and CAC.

Verification / Alternative check:
Any codon table confirms His = CAU/CAC; Tyr = UAU/UAC; Stop = UAA/UAG/UGA; Met = AUG; Ile = AUU/AUC/AUA.

Why Other Options Are Wrong:

• UAA/UAC: stop vs tyrosine.
• AUG/AUA: methionine vs isoleucine.
• UUA/UUC: leucine vs phenylalanine.

Common Pitfalls:
Assuming similarity in two-letter prefixes guarantees the same amino acid; third-position wobble does not always ensure synonymy.

Final Answer:
CAU and CAC