Which characteristic of the genetic code lowers the likelihood of mutation?

Degeneracy

Degeneracy simply means that most of the amino acids produced during protein synthesis from DNA is coded by more than one codon. A codon is a sequence of 3 nucleotides that codes for a specific amino acid.

Because more than 1 codon can produce the same amino acid, the chances of having the synthesis of proteins affected by mutations (i.e. point mutations) is decreased. For example, if the codon with the nucleotide series GAA, which codes for the amino acid glutamate, becomes the codon GAG, the codon will still produce glutamate because the code is degenerate.