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Modern Evolutionary Classification

Modern Evolutionary Classification . Section 18-2. Which Similarities are Most Important?. Taxonomic groups above species were “invented” to distinguish between one family, phylum, etc., and another

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Modern Evolutionary Classification

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  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 • Taxonomists have always tried to group organisms according to biologically important characteristics

  3. Grouping organisms based on visible similarities and differences has its drawbacks • 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 • Prompted by Darwin and his descent with modification • 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 • Reasoning: all members of a genus share a common ancestor

  6. What this means… • 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 • Similar shells, hole in shell, attached to rocks

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

  9. Classification Using Cladograms • Shift made from evolutionary classification to cladistic analysis • 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 • Diagram that shows evolutionary relationships • Shows how one lineage branched into others

  11. 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

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

  13. Similarities in DNA and RNA • 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 • More similar DNA sequences - more recently shared common ancestor

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

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

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