The genetic code is universal. The same codons specify the same amino acids in virtually every organism on Earth—from bacteria to humans.
This universality is profound evidence that all life shares a common ancestor.
64
possible codons (4³)
20
amino acids they encode
3
stop codons (UAA, UAG, UGA)
Because 64 codons map to only 20 amino acids + stop signals, the code is redundant. Multiple codons can specify the same amino acid. This redundancy provides some protection against mutations.
The code was cracked in the 1960s by Marshall Nirenberg and others—one of biology's greatest intellectual achievements.