Wobble effect

According to experiments with synthetic polynucleotides, it is often sufficient if the first two of the three bases of a codon are the same. Thus, the codons GCU, GCC, GCA, and GCG all incorporate alanine. Genetically, this wobble effect leads to a lowering of the frequency of mutation, i.e., a stabilization of the species. 

There may be no detectable effect because of the degeneracy of the code. This would be more likely if the changed base in the mRNA molecule were to be at the third nucleotide of a codon such mutations are often referred to as silent mutations. Because of wobble, the translation of a codon is least sensitive to a change at the third position. 

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