How many total codon combinations exist in the genetic code?

The total number of codon combinations in the genetic code is 64. This is derived from the fact that codons are sequences of three nucleotides, and since there are four different nucleotides (adenine, cytosine, guanine, and uracil in RNA; and thymine in DNA), the total number of possible combinations can be calculated as 4 raised to the power of 3.

Mathematically, this is expressed as 4^3, which equals 64 (4 x 4 x 4). Each of these codons corresponds to specific amino acids or serves as a stop signal during protein synthesis. Out of these, 61 codons code for amino acids, while 3 codons are stop codons, indicating the end of protein synthesis. Therefore, while 20 refers to the number of standard amino acids that these codons code for, the correct total number of codon combinations available in the genetic code is indeed 64.