7.9: Phylogeny

Phylogeny

• the study of evolutionary relationships

• depicted on cladograms/phylogenetic trees

• cladograms and phylo trees both show evolutionary relationships but…

  • clado → do not indicte time or “amount” of difference, usually just based on physical traits

  • phylo. trees → indicate time spans between branching pts, usually based on molecular DNA

• Terminology:

  • taxon: the species of interest

  • branch: represents the evolutionary history of the taxon

  • node: represents the most recent common ancestor (MRCA) b/t 2 species

  • root: the oldest common ancestor of the species on the tree

  • ancestral character: shared among all decendents from the root

  • derived character: shared among specific descendants, not all

  • outgroup: least closely related organism

  • Monophyletic taxon (clade)

    • defined by shared characteristics inherited from a common ancestor

    • includes all descendants of that common ancestor

  • Polyphyletic taxon

    • defined by shared characteristics that arise through convergent evolution

    • do not share a very recent common ancestor

    • Paraphyletic taxon

      • includes some, but not all, descendants of a common ancestor

      • are defined by the ancestral characteristics that they share

      • often described as a “lineage”

• another common way to show relationships is with classification

  • organisms in smaller more specific groups are more closely related