The first codon was deciphered in 1961 by Marshall Nirenberg of the National Institutes of Health. He synthesized an mRNA by linking only uracil-bearing RNA nucleotides, resulting in UUU codons. Nirenberg concluded that the mRNA codon UUU specifies the amino acid phenylalanine. More elaborate techniques allowed investigators to determine all 64 codons by the mid-1960's. There is redundancy in the genetic code, but no ambiguity.
Ambiguity is absent, since codons code for only one amino acid.
The correct ordering and grouping of nucleotides is important in the molecular language of cells. This ordering is called the reading frame .