Semantides

Semantides (or semantophoretic molecules) are biological macromolecules that carry phylogenetic information about evolutionary history. Semantides may be further classified into three categories: the genes themselves are known as 'primary semantides' , the mRNA transcripts 'secondary semantides', and polypeptides 'tertiary semantides'. The terms were coined by Linus Pauling and Emile Zuckerkandl and used to contrast to episemantic and aposemantic molecules when discussing the phylogenetic evolutionary history contained in macromolecular sequences.^[1] Although semantides are the major type of data used in modern phylogenetics the term itself is not commonly used.

The macromolecules chosen are usually common to all cells, used in phylogeny because they change slowly over time. Examples of these molecules are:

• rRNA/rDNA
• RNase P RNA
• ATPase
• RecA protein (involved in genetic recombination)
• Cytochrome C
• Heat shock protein genes

The above semantides can yield different phylogenetic trees, but if the genetic relatedness is correct for 2 or more, that correlation could mean that the evolutionary tree is correct.

References