1. Modern Evolutionary Classification Section 18-2

2. Which Similarities are Most Important? Taxonomic groups above species were “invented” to distinguish between one family, phylum, etc., and another Taxonomic groups above species were “invented” to distinguish between one family, phylum, etc., and another Taxonomists have always tried to group organisms according to biologically important characteristics Taxonomists have always tried to group organisms according to biologically important characteristics

3. Grouping organisms based on visible similarities and differences has its drawbacks Grouping organisms based on visible similarities and differences has its drawbacks Ex. Dolphins Ex. Dolphins  Fish? - live in water, have finlike limbs  Mammal? - breathe air and feed young

4. Evolutionary Classification Phylogeny - study of evolutionary relationships among organisms Phylogeny - study of evolutionary relationships among organisms  Prompted by Darwin and his descent with modification Organisms grouped into categories that represent evolutionary descent Organisms grouped into categories that represent evolutionary descent  Evolutionary classification

5. What this means… Species in a genus are more closely related to each other than they are with species of another genus Species in a genus are more closely related to each other than they are with species of another genus  Reasoning: all members of a genus share a common ancestor

6. What this means… All genera in a family share a common ancestor All genera in a family share a common ancestor  Ancestor is further in past than ancestor of any genus in family

7. Crustacean or Mollusks? Limpets and barnacles first classified on visible similarities Limpets and barnacles first classified on visible similarities  Similar shells, hole in shell, attached to rocks

8. Crustacean or Mollusks? Barnacles - molt (shed exoskeleton), have joined limbs, body segments Barnacles - molt (shed exoskeleton), have joined limbs, body segments Limpets - internal anatomy like snails, don’t molt Limpets - internal anatomy like snails, don’t molt Barnacles are crustaceans, limpets are mollusks Barnacles are crustaceans, limpets are mollusks

9. Classification Using Cladograms Shift made from evolutionary classification to cladistic analysis Shift made from evolutionary classification to cladistic analysis Uses characteristics that are “evolutionary innovations” or new characteristics that arose as lineages evolve over time Uses characteristics that are “evolutionary innovations” or new characteristics that arose as lineages evolve over time  called derived characteristics - not found in older lineages

10. Classification Using Cladograms Can use derived characteristics to construct a cladogram Can use derived characteristics to construct a cladogram  Diagram that shows evolutionary relationships  Shows how one lineage branched into others

12. Similarities in DNA and RNA Because DNA and RNA are so similar across all forms of life, these molecules provide an excellent way of comparing organism Because DNA and RNA are so similar across all forms of life, these molecules provide an excellent way of comparing organism

13. Similarities in DNA and RNA Genes show important similarities at the molecular level Genes show important similarities at the molecular level DNA similarities can be used the help determine classification and evolutionary relationships DNA similarities can be used the help determine classification and evolutionary relationships

14. Similarities in DNA and RNA Scientists can compare DNA sequences to trace history of genes over millions of years Scientists can compare DNA sequences to trace history of genes over millions of years DNA evidence can show evolutionary relationships of species and how species have changed DNA evidence can show evolutionary relationships of species and how species have changed  More similar DNA sequences - more recently shared common ancestor

15. Molecular Clocks Comparisons of DNA can be used to mark the passage of evolutionary time Comparisons of DNA can be used to mark the passage of evolutionary time Done with molecular clocks Done with molecular clocks  Uses DNA comparisons to estimate length of time two species have been evolving independently

16. Molecular Clocks By analyzing neutral gene mutations, and looking for dissimilarities, one can tell how long ago they shared a common ancestor By analyzing neutral gene mutations, and looking for dissimilarities, one can tell how long ago they shared a common ancestor