Modern Evolutionary Classification 18-2

Evolutionary Classification The strategy of grouping organisms together based on their evolutionary descent or Phylogeny. A. Phylogeny – Scientist group organisms into categories that represent lines of evolutionary decent or evolutionary relationships among organisms, not just by physical similarities. B. The higher the level of the taxon the further back in time the common ancestor would be in that taxon. C. Animals that appear very similar may not share a recent common ancestor, at all. Example – Dolphin and Shark.

Plant Phylogeny

Animal (Invertebrate) Phylogeny

Animal (Vertebrate) Phylogeny

II. Classification Using Cladogram A. Derived Characters– Identifies and considers only those characteristics that appear in recent parts of a lineage not in older members. These are called Derived characters. 1. Cladogram – Uses Derived characters to construct a Cladogram diagram that shows evolutionary relationships among a group of organisms.

III. Similarities of DNA and RNA A. The more similar the DNA sequence of two species , the more recently they shared a common ancestor and the more closely they are related in evolutionary terms.

VI. Molecular Clock A. Uses DNA to estimate the length of time that 2 species have been evolving independently or have been separated. B. The longer in time 2 species descended from a common ancestor, the more different their genes are likely to be.