1.14 Why are organisms classified into groups ?

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1.14 Why are organisms classified into groups ?

  1. 1. AIM: Why are organisms classified into groups? Warm – up: Complete Exercise 3 in Lab
  2. 2. Necessary Terms Taxonomy is the classification of organisms. Most biologists feel that classification should be based upon phylogeny. Phylogeny is the ancestry of organisms- how organisms are related by evolution Systematics is the study of phylogeny. Cladistics is a means of understanding the phylogeny of organisms.
  3. 3. Phylogeny and Biochemistry • Phylogeny of many groups has been studied by comparing structures of proteins or other biochemicals (DNA, RNA) What about mutations?
  4. 4. Molecular Clocks • Estimate time of divergence by comparing numbers of neutral mutations in DNA, which tend to accumulate in the DNA of a lineage at a fairly constant rate. • 70,000 years ago, Euro – Japanese split • 140,000 African – EuroJapanese split • 5 mya – human – chimps split
  5. 5. Biochemistry and Common Ancestry • All use DNA (or RNA) as genetic material • All use same universal genetic code • All use same 20 amino acids in building proteins • All use left, not right handed amino acids) What does this information tell us?
  6. 6. Cladistics and Taxonomy
  7. 7. Classification in Biology
  8. 8. Classification in Biology Arranging living organisms into groups
  9. 9. Classification in Biology Arranging living organisms into groups
  10. 10. Classification in Biology Arranging living organisms into groups WHY BOTHER?
  11. 11. Classification in Biology Arranging living organisms into groups WHY BOTHER? 1. Species Identification: Easier to find out to which species an organism belong to if everything is organized
  12. 12. Classification in Biology Arranging living organisms into groups WHY BOTHER? 1. Species Identification: Easier to find out to which species an organism belong to if everything is organized 2. Predictive Value: If several members of a group have a particular characteristic, another species in this group may also have this characteristic
  13. 13. Classification in Biology Arranging living organisms into groups WHY BOTHER? 1. Species Identification: Easier to find out to which species an organism belong to if everything is organized 2. Predictive Value: If several members of a group have a particular characteristic, another species in this group may also have this characteristic 3. Evolutionary Links: Species in the same group probably share characterstics because they have evolved from a common ancestor
  14. 14. Hierarchical classification Carolus Linnaeus Binomial nomenclature
  15. 15. Seven basic categories of biological classification More categories are added to recognize similarities among groups of taxa within these levels, for example superfamilies, etc. Kingdom Phylum Class Order Family Genus Species
  16. 16. Kingdom
  17. 17. Kingdom Phylum
  18. 18. Kingdom Phylum Class
  19. 19. Kingdom Phylum Class Order
  20. 20. Kingdom Phylum Class Order Family
  21. 21. Kingdom Phylum Class Order Family Genus
  22. 22. Kingdom Phylum Class Order Family Genus Species
  23. 23. Classification of Humans
  24. 24. Classification of Humans Kingdom (Animalia)
  25. 25. Classification of Humans Kingdom (Animalia) Phylum (Chordata)
  26. 26. Classification of Humans Kingdom (Animalia) Phylum (Chordata) Class (Mammalia)
  27. 27. Classification of Humans Kingdom (Animalia) Phylum (Chordata) Class (Mammalia) Order (Primates)
  28. 28. Classification of Humans Kingdom (Animalia) Phylum (Chordata) Class (Mammalia) Order (Primates) Family (Hominidae)
  29. 29. Classification of Humans Kingdom (Animalia) Phylum (Chordata) Class (Mammalia) Order (Primates) Family (Hominidae) Genus (Homo)
  30. 30. Classification of Humans Kingdom (Animalia) Phylum (Chordata) Class (Mammalia) Order (Primates) Family (Hominidae) Genus (Homo) Species (Homo sapiens)
  31. 31. Artificial vs. Natural Classification • Natural Classification: matches evolutionary origins of the species in the group • Artificial classification: Help with species identification but have no other value… ex. Insects, birds, bats are put in the same group. WHY?
  32. 32. Convergent evolution and analogous structures: Not all similarity represents common ancestry! The Ocotillo (SW U.S.A) and Allauidia (Madagascar) are not closely related. Resemblance due to independent adaptations to similar environmental pressures.
  33. 33. Organisms with homologous structures should be classified in the same group because they have a common ancestry, even if they look different!
  34. 34. Homology vs. Analogy • Homology refers to having a trait in common because it has been inherited from a common ancestor. – CLADOGRAMS BASED ON HOMOLOGIES • Species can also evolve the same traits independently. Independent evolution of the same characteristic is called convergent evolution and those traits are called analagous.
  35. 35. Cladograms and Classification Classification of many groups has been re-examined using cladograms. In many cases, cladograms have confirmed existing classifications. Not surprising since both traditional classification and cladistics attempt to reflect phylogeny. Cladograms can be difficult to reconcile with traditional classifications, because the nodes can occur at any point. It can therefore seem rather arbitrary how the hierarchy of taxa is fitted to the clades. In some cases, cladistics suggests radically different phylogenies. The strength of cladistics is that the comparisons between organisms are objective, based on molecular differences. The weakness is that molecular differences are analyzed on the basis of probabilities. Occasionally, improbable events occur makine the analysis wrong. Therefore, cladistics should not be treated as infallible. However, it can stimulate a reinterpretation of the data on which traditional classifications have been based.
  36. 36. Cladogram: A phylogenetic diagram that classifies organisms according to shared
  37. 37. Cladogram: A phylogenetic diagram that classifies organisms according to shared Clade: Group of organisms that evolved from a common ancestor (the ancestor plus all its descendants)
  38. 38. Cladogram: A phylogenetic diagram that classifies organisms according to shared Clade: Group of organisms that evolved from a common ancestor (the ancestor plus all its descendants) Cladistics: method of classification of living organisms based on construction and analysis of cladograms
  39. 39. Connection between classification
  40. 40. Constructing a Cladogram
  41. 41. Constructing a Cladogram Ancestral (=homologous) trait: A trait shared due to common ancestry
  42. 42. Constructing a Cladogram Ancestral (=homologous) trait: A trait shared due to common ancestry Derived trait: A trait that differs from a common ancestor
  43. 43. Cats are more similar to dogs than they are to frogs, because they share a more recent common ancestor with dogs
  44. 44. An outgroup is used to decide which characteristics are ancestral Ingroup Outgroup
  45. 45. Procedure 1: Classifying Doodlebirds ?
  46. 46. Why are legs, beak and crest not useful in the analysis?
  47. 47. (outgroup) Web toes, Three tails
  48. 48. TAXA Petal no. Leaf Seed shape A 5 compound flat B 4 compound round C 4 simple round D 5 compound round Outgroup 4 simple round
  49. 49. A B C D A 1 (compound) 0 2 (compound, 5) B 0 1 (compound) C 0 D

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