Final answer:
Each codon specifies only one amino acid, and the genetic code is unambiguous. However, due to redundancy, one amino acid may be coded by more than one codon. This feature, known as degeneracy, protects against the effects of mutations.
Step-by-step explanation:
The genetic code is unambiguous, meaning a single codon specifies only one amino acid. However, the genetic code is also redundant, as a single amino acid can be encoded by multiple codons. For instance, the amino acid threonine is coded for by four different codons. This redundancy is known as degeneracy, and it serves as a protective mechanism against mutations, especially at the third nucleotide position of a codon, often called the 'wobble position'. In some cases, a change in this wobble position does not alter the amino acid that is incorporated into the protein.
An example of this degeneracy is glycine, which is specified by four codons: GGU, GGC, GGA, and GGG. The universal nature of the genetic code is highlighted by the codon AUG, which has a dual role. In the interior of a sequence of codons, it specifies methionine, and at the start of an mRNA strand, it signals the initiation of protein synthesis. It's worth noting that while most amino acids have multiple codons, two exceptions are tryptophan and methionine, as each is encoded by only one codon.