We consider in general two-block substitutions and their fixed points. prove that some of them have a simple structure: points are morphic sequences. Others intrinsically more complex, such as the Kolakoski sequence. this for Thue-Morse sequence base 3/2.

Two simple methods for estimating the numbers of synonymous and nonsynonymous nucleotide substitutions are presented. Although they give no weights to different types of codon substitutions, these methods give essentially the same results as those obtained by Miyata and Yasunaga's and by Li et al.'s methods. Computer simulation indicates that estimates of synonymous substitutions obtained by th...