Figure 4

Amino acids distribution and chronological models for the recruitment into the genetic code. Factorial plane representation and species colour coding symbols are as in Figure 1. Dashed diagonal line in grey separates roughly the territory T1 ([high optimal growth temperature]-[high GC content]) from the territory T2 ([moderate optimal growth temperature]-[low GC content]), with arrow pointing from T1 to T2. Colour coding for amino-acids is following the model of Jordan et al. [9]: "strong losers" are orange (Glu, Gly, Ala, Pro); "weak loser" Lys is orange with a black outline; "strong gainers" are filled black (Cys, Ser, His, Phe, Met); "weak gainers" have black outlines (Asn, Ile, Thr, Val); all other amino acids are green. Amino acids found in Miller's experiments [14] or in the Murchison meteorite [15] are labelled with black, respectively red, crosses (the number of crosses, in each colour, follows the reported abundances for the corresponding amino acids; see Additional Table 3 in Jordan et al. [9]). Numbering of amino acids in blue is following the chronology compiled by Trifonov (Figure 1 in [10]; with possible different codon chronologies associated with a given amino acid, such as for Ser ranking 6 or 11 following the codon).