Which statement describes the degeneracy of the genetic code?

• A. Most amino acids are encoded by more than one codon.
• B. Each amino acid is encoded by exactly one codon.
• C. The code uses stop codons for all amino acids.
• D. There are no redundant codons.

Answer: (A)

Degeneracy of the genetic code means that many amino acids can be specified by more than one codon. In the standard code, there are 64 codons but only 20 amino acids (plus stop signals), so several amino acids have multiple codons that encode them. For example, leucine, serine, and arginine are each specified by six different codons. The same amino acid can often be encoded by codons that differ in the third position, a flexibility known as wobble, which is a key reason for this redundancy.

This redundancy helps protect against mutations: a single-nucleotide change in a codon may still yield the same amino acid and a similar protein sequence, making the code more robust. The other statements don’t fit because one amino acid is not limited to a single codon, stop codons exist to terminate translation, and there are certainly redundant codons in use.