The genetic code is universal because all species use the same four bases A,T,C and G, and each base sequence codes for the same amino acid in all species. despite the 64 possible codons (sequence of three bases), there are only 20 possible amino acids. This means that multiple codons code for one amino acid, meaning the code is degenerate. Overlapping refers to how the code is read. The first three bases are read as one codon, then the next three as the second etc, therefore each base is read only once and the bases do not overlap.