Biology

1. Biology Copyright Pearson Prentice Hall

2. 18-2 Modern Evolutionary Classification Copyright Pearson Prentice Hall

3. EvolutionaryClassification • Linnaeus grouped species into larger taxa mainly according to visible similarities and differences. • How are evolutionary relationships important in classification? Copyright Pearson Prentice Hall

4. Evolutionary Classification • Evolutionary Classification • Phylogeny is the study of evolutionary relationships among organisms. Copyright Pearson Prentice Hall

5. Evolutionary Classification • Biologists currently group organisms into categories that represent lines of evolutionary descent, or phylogeny, not just physical similarities. • The strategy of grouping organisms is based on evolutionary history and is called evolutionary classification. Copyright Pearson Prentice Hall

6. Evolutionary Classification • The higher the level of the taxon, the further back in time is the common ancestor of all the organisms in the taxon. • Organisms that appear very similar may not share a recent common ancestor. Copyright Pearson Prentice Hall

7. Evolutionary Classification • Different Methods of Classification Mollusk Crustaceans Conical Shells Appendages Crab Barnacle Limpet Barnacle Limpet Crab Molted external skeleton Tiny free-swimming larva Segmentation CLASSIFICATION BASED ON VISIBLE SIMILARITY CLADOGRAM Copyright Pearson Prentice Hall

8. Evolutionary Classification • Superficial similarities once led barnacles and limpets to be grouped together. Conical Shells Appendages Crab Barnacle Limpet Copyright Pearson Prentice Hall

9. Evolutionary Classification • However, barnacles and crabs share an evolutionary ancestor that is more recent than the ancestor that barnacles and limpets share. • Barnacles and crabs are classified as crustaceans, and limpets are mollusks. Copyright Pearson Prentice Hall

10. Classification UsingCladograms • Classification Using Cladograms • Many biologists now use a method called cladistic analysis. • Cladistic analysis identifies and considers only new characteristics that arise as lineages evolve. • Characteristics that appear in recent parts of a lineage but not in its older members are called derived characters. Copyright Pearson Prentice Hall

11. Classification UsingCladograms • Derived characters can be used to construct a cladogram, a diagram that shows the evolutionary relationships among a group of organisms. • Cladograms help scientists understand how one lineage branched from another in the course of evolution. Copyright Pearson Prentice Hall

12. Classification UsingCladograms • A cladogram shows the evolutionary relationships between crabs, barnacles, and limpets. Crustaceans Mollusk Barnacle Limpet Crab Molted external skeleton Segmentation Tiny free-swimming larva Copyright Pearson Prentice Hall

13. Similarities in DNAand RNA • Similarities in DNA and RNA • How can DNA and RNA help scientists determine evolutionary relationships? Copyright Pearson Prentice Hall

14. Similarities in DNA and RNA • The genes of many organisms show important similarities at the molecular level. • Similarities in DNA can be used to help determine classification and evolutionary relationships. Copyright Pearson Prentice Hall

15. Similarities in DNA and RNA • DNA Evidence • DNA evidence shows evolutionary relationships of species. • 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. Copyright Pearson Prentice Hall

16. Molecular Clocks • Molecular Clocks • Comparisons of DNA are used to mark the passage of evolutionary time. • A molecular clock uses DNA comparisons to estimate the length of time that two species have been evolving independently. Copyright Pearson Prentice Hall

17. Molecular Clocks A gene in an ancestral species • Molecular Clock 2 mutations 2 mutations new mutation new mutation new mutation Species Species Species A C B Copyright Pearson Prentice Hall

18. Molecular Clocks • A molecular clock relies on mutations to mark time. • Simple mutations in DNA structure occur often. • Neutral mutations accumulate in different species at about the same rate. • Comparing sequences in two species shows how dissimilar the genes are, and shows when they shared a common ancestor. Copyright Pearson Prentice Hall

19. 18-2 Copyright Pearson Prentice Hall

20. 18-2 • Grouping organisms together based on their evolutionary history is called • evolutionary classification. • traditional classification. • cladogram classification. • taxonomic classification. Copyright Pearson Prentice Hall

21. 18-2 • Traditional classification groups organisms together based on • derived characters. • similarities in appearance. • DNA and RNA similarities. • molecular clocks. Copyright Pearson Prentice Hall

22. 18-2 • In an evolutionary classification system, the higher the taxon level, • the more similar the members of the taxon become. • the more common ancestors would be found in recent time. • the fewer the number of species in the taxon. • the farther back in time the common ancestors would be. Copyright Pearson Prentice Hall

23. 18-2 • Classifying organisms using a cladogram depends on identifying • external and internal structural similarities. • new characteristics that have appeared most recently as lineages evolve. • characteristics that have been present in the group for the longest time. • individual variations within the group. Copyright Pearson Prentice Hall

24. 18-2 • To compare traits of very different organisms, you would use • anatomical similarities. • anatomical differences. • DNA and RNA. • proteins and carbohydrates. Copyright Pearson Prentice Hall

25. END OF SECTION