The last universal common ancestor is the single ... scientists (its letter designation is W). “[T]here is scientific consensus that W was the last of the 20 canonical amino acids to be added ...

To assess the level of background inclusion, the researchers treated cells with different tRNA that carried a traceable amino acid and recognized either the TCG codon or one of the other six least ...

The genetic code is a set of three-letter combinations of nucleotides ... Although each codon is specific for only one amino acid (or one stop signal), the genetic code is described as degenerate ...

However, with only 20 amino acids, a triplet code would also suggest redundancy–in other words, more than one codon might correspond to the same amino acid, or there might even be "spare" or ...