Fig. 20. (A) Dependence of guanine composition at the first codon position (G1) upon GC content of a gene. The rectangular surrounding dots of G1 shows the border line of the possible G1 composition, when genes can be used to any sequence in the sequence space. (B) Correlation of base compositions in the codon with GC content of a gene. The straight lines indicate average changes of guanine, adenine, cytosine and thymine compositions at the first (B1), second (B2) and third (B3) base positions in the codon, respectively.