If the genetic code contained only three different bases instead of four, and these bases made up 3-base code words (codons), how many different codons would be possible?

27

Explanation:

Genetic code has a different combination of four different bases. Each genetic code is made up of three nucleotides. Therefore, either of the four bases may be present in a genetic code at three different positions. This gives a total of 4^3 = 64 different genetic codes to specify amino acids. If there were only three bases in genetic code, either of the three bases may be present at each position of the triplet codon. This would give a total of 3 x 3 x 3 = 27 different genetic codes to code for different amino acids.