Answer: 20 amino acids
Explanation:
The triplet nature of the genetic code make for a possible 64 codons: 61 code for amino acids present in most polypeptide chains while the remaining 3 are special-sense codons, since they only signal for the termination of the polypeptide chain.
Thus, due to the degeneracy of the genetic code, the 64 codons code for 20 amino acids