[Objective]The aim was to research the relationship between nucleotide substitutions rate and selective pressure.[Method]Synonymous and nonsynonymous substitutions and their ratios for some sorghum and maize genes in nucleus and organelle genomes were analyzed by statistical method,and comparative analysis of related functional genes were carried out.[Result]The pure selective pressures of the related functional genes were similar between nucleus and chloroplast genomes,but was lower in mitochondrial genome.The significant differences of nucleotide substitution rate between sorghum and maize orthologous genes in nucleus genome,and among different functional genes in nucleus genome were mainly due to the nonsynonymous substitution difference.[Conclusion]The molecular evolutional rate of different functional genes and different lineages were influenced by selective pressure.The differences of molecular evolutional rate among nucleus,chloroplast and mitochondria genomes had no direct relationship with selective pressure.
