Most used codons per amino acid in humans [in black rectangles] compared to a plant Arabidopsis thaliana [in white smaller rectangles]. The codons that are the most used by both organisms [in double rectangle, external black for man and inner white for the plant], are the unique codons for amino acid Met (M), and for Trp (W), respectively, plus the basics: one Arg (R) AGA and one Lys AAG, and the stop codon UGA. Humans use equally two codons for one amino acid: Arg AGA and Arg AGG. The color for the rest of the codons has been removed to make comparisons easier (database used: Nakamura et al., 2000).