ABSTRACT
It is not too much to say that molecular biology, including genome research, has progressed based on the determination of nucleotide or amino acid sequences. However, these ap-proaches are limited to the analysis of relatively small numbers of the same genes among spe-cies. On the other hand, by graphical presenta-tion of the ratios of the numbers of amino acids present to the total numbers of amino acids presumed from the target gene(s) or genome or those of the numbers of nucleotides present to the total numbers of nucleotides calculated from the target gene(s) or genome, we can readily draw conclusions from extraordinarily huge data sets integrated by human intelli-gence.
1) Assuming polymerization of amino acids or nucleotides in a simulation analysis based on a random choice, proteins were formed by simple amino acid polymerization, while nucleotide polymerization to form nucleic acids encoding specific proteins needed certain specific control. These results proposed that protein formation chronologically preceded codon formation during the establishment of primitive life forms. In the prebiotic phase, amino acid composition was a dominant factor that determined protein characteristics; the “Amino Acid World”.
2) The genome is constructed homogeneou- sly from putative small units displaying similar codon usages and coding for similar amino acid compositions; the unit is a gene assembly en-coding 3,000 - 7,000 amino acid residues and this unit size is independent not only of genome size, but also of species.
3) In codon evolution, all nucleotide alterna-tions are correlated, not only in coding regions, but also in non-coding regions; the correlations can be expressed by linear formulas; y = ax + b, where “y” and “x” represent nucleotide con-tents, and “a” and “b” are constant.
4) The basic pattern of cellular amino acid compositions obtained from whole cell lysates is conserved from bacteria to Homo sapiens, and resembles that calculated from complete genomes. This basic pattern is characterized by a “star-shape” that changes slightly among species, and changes in amino acid composi-tion seem to reflect biological evolution.
5) Organisms can essentially be classified according to two codon patterns.
Biological evolution due to nucleotide sub-stitutions can be expressed by simple linear formulas based on mathematical principles, while natural selection must affect species pre- servation after nucleotide alternations. There-fore, although Darwin’s natural selection is not directly involved in nucleotide alternations, it contributes obviously to the selection of nu-cleotide alternations. Thus, Darwin’s natural selection is doubtless an important factor in biological evolution.