Final answer:
Proflavin was used to test the triplet code hypothesis in an experiment conducted by Francis Crick and Sydney Brenner. They found that amino acids must be specified by groups of three nucleotides, which are called codons.
Step-by-step explanation:
Proflavin was used to test the triplet code hypothesis in an experiment conducted by Francis Crick and Sydney Brenner. They used proflavin, a chemical mutagen, to insert one, two, or three nucleotides into a viral gene. They found that when one or two nucleotides were inserted, normal proteins were not produced. But when three nucleotides were inserted, the protein was synthesized and functional. This experiment demonstrated that amino acids must be specified by groups of three nucleotides, which are called codons.