Information stored in the nucleotide sequence was present in some type of genetic code. Mrna is the intermediate in the flow of info. Each amino acid is encoded by three sequential nucleotide codons. Codons must contain at least 3 successive nucleotides. Degenerate : an amino acid that is specified by more than one codon. Codes are highly degenerate, because only 3 of the 64 conde have special function -- termination codes. Evidence suggest that same amino acids were being encode by different sequence, which would make the code degenerate. First attempt: polyribonucleotide consisting only uridine --polyu) -- found to be coding for phenylalanine. Some minor deviation that evolved as secondary changes -- they are considered universal- present in all organisms. Indicate that all known organisms present on earth today share a common evolutionary origin. Synonymous: a change in the nucleotide that does not affect amino acid sequence. Nonsynonymous: change that causes an amino acid substitution.