We estimated the theoretical relations between amino acid replacement ratio α and nucleotide substitution ratio β. Three types of relations, α_<max>(upper limit of α),α_<min>(lower limit of α) and α_<ave>(average of α) to β　were calculated for 6 types of amino acid groups respectively.
The profile of α-β plots obtained from the sequence data of 16 histone H4 genes from GenBank was similar to the α_<min>-β relationship.