Genetic code was discovered by

Genetic code was discovered by Holley, Nirenberg and Khorana.
Marshall Nirenberg, Har Gobind Khorana, and their colleagues were the first to determine the genetic code and show how the nucleic acid bases determine the sequence of the 20 different amino acids during protein synthesis.
Each gene's code uses the four nucleotide bases of DNA: adenine (A), cytosine (C), guanine (G) and thymine (T) in various ways to spell out three-letter “codons” that specify which amino acid is needed at each position within a protein.