How many nucleotide bases make up a codon?

The nucleotide triplet that encodes an amino acid is called a codon. Each group of three nucleotides encodes one amino acid. Since there are 64 combinations of 4 nucleotides taken three at a time and only 20 amino acids, the code is degenerate (more than one codon per amino acid, in most cases).

the darker peppered moth species were favored due to the fact that the industrial revolution had made all the nearby trees a darker color instead of white.