Molecular clock

"Different types of molecules are discussed in relation to their fitness for providing the basis for a molecular phylogeny. Best fit are the "semantides", i.e. the different types of macromolecules that carry the genetic information or a very extensive translation thereof. The fact that more than one coding triplet may code for a given amino acid residue in a polypeptide leads to the notion of "isosemantic substitutions" in genic and messenger polynucleotides. Such substitutions lead to differences in nucleotide sequence that are not expressed by differences in amino acid sequence. Some possible consequences of isosemanticism are discussed"