Fig. 28. Computer simulation of the evolution of genes originated from a GC-rich ancestral gene. The simulation was carried out by using a GC-NSF(a) of a M. tuberculosis GC-rich gene composed of 1,500 bases as an ancestor gene. Mutations were introduced at a probability of 1% on every base position at every step. When aˇˇˇˇprotein encoded by the mutated sequence satisfied 6 conditions required to form polypeptide sequence into appropriate three-dimensional structure, the gene was selected as an active gene. If it does not, introduction step of mutation was repeated from one step before. The simulation of gene evolution was carried out under 9 different mutation pressures. Only guanine composition at the first codon position (G1) was largely deviated from the approximated linear line drawn by using seven microbial genome data out of twelve base compositions. Therefore, G1 composition is only given as an example of results of the gene simulation in this Figure.