Phylogeny and Cladistics

Which similarities are most important? It’s not always easy to tell! Evolutionary classification – classifying based on phylogeny, not just structural characteristics. Phylogeny – the study of evolutionary relationships among organisms.

Classification using Cladograms Many biologists now use a method called cladistic analysis. Cladistic analysis identifies and considers only new characteristics that arise as lineages (new line of organisms) evolve. Characteristics that appear in recent parts of a lineage but not in its older members are called derived characters.

Cladogram

Cladogram

Check out this cladogram!

Quick Lab p 453 Complete the Quick Lab neatly to be added to your Lab book. Title: How is a Cladogram constructed? Procedure: a) Copy the chart titled “Derived Characters in Organisms” b) Identify the organism that is least closely related to the others. c) Construct a cladogram that includes the animals names and the appropriate derived characters Analyze and Conclude: Answer the four questions in complete sentences Put your completed lab in your lab book and drop it in the drawer.

Let’s make a Cladogram Cladogram

Other Characteristics used to indicate Evolutionary connection Similarities in DNA can be used to help determine classification and evolutionary relationships. The more similar the DNA of two species, the more recently they shared a common ancestor, and the more closely they are related in evolutionary terms. The more two species have diverged from each other, the less similar their DNA will be. Read DNA Evidence on p. 454 looking at Figure 18-8.

Other Characteristics used to indicate Evolutionary connection Molecular Clocks – monitor “neutral” mutations that help estimate the length of time two species have been evolving independently. Read Molecular Clocks on p. 455. - In your notes, compare Positive, Negative and Neutral mutations.

Molecular Clocks Which species appear to be most closely related? Where is Species B and C’s most recent ancestor? Where is Species A and C’s most recent ancestor? Let’s go back to our earlier animation Cladogram

Other Characteristics used to indicate Evolutionary connection Similarities in Embryological Development

Modern Taxonomist’s Criteria Similarities and differences in structure Homologous structures – same structure but different function Indicate evolutionary connection Phylogeny Similarities in DNA/RNA Molecular Clocks Similarities in Embryological development