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Classification

Classification

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Classification

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  1. Classification Ch 20

  2. Taxonomy • Branch of biology concerned with identifying, naming, and classifying organisms • Began with the ancient Greeks and Romans • Aristotle classified organisms into groups such as horses, birds, and oaks • John Ray (1627–1705) • Believed that each organism should have a set name • Otherwise, “men…cannot see and record accurately.”

  3. Classifying Organisms

  4. Taxonomy:Binomial System • Mid-eighteenth century, Linnaeus developed the binomial system of nomenclature • First word is genus name • Second word is specific epithet • Refers to one species (of potentially many) within its genus • A species is referred to by the full binomial name (Genus species) • Genus name can be used alone to refer to a group of related species

  5. Carolus Linnaeus

  6. Taxonomy:Distinguishing Species • Distinguishing species on the basis of structure can be difficult • Members of the same species can vary in structure • Attempts to demonstrate reproductive isolation is problematic because: • Some species hybridize, and • Reproductive isolation is difficult to observe

  7. Members of a Species

  8. Hybridization between species

  9. Classification Categories • Modern taxonomists use the following classification: • Species • Genus – one or more species • Family – one or more genera • Order – one or more families • Class – one or more orders • Phylum – one or more classes • Kingdom – one or more phyla • Domain – one or more kingdoms

  10. Hierarchy of Taxa forParthenocissus quinquefolia

  11. Classification Categories • The higher the category, the more inclusive • Organisms in the same domain have general characteristics in common • In most cases, classification categories can be subdivided into additional categories • Superorder • Order • Suborder • Infraorder

  12. Phylogenetic Trees • Systematics - the diversity of organisms at all levels • One goal of systematics is to determine phylogeny (evolutionary history) of a group • Phylogeny often represented as a phylogenetic tree • A diagram indicating lines of descent • Each branching point: • Is a divergence from a common ancestor • Represents an organism that gives rise to two new groups

  13. Classification and Phylogeny

  14. Phylogenetic Trees • Classification lists the unique characters of each taxon and is intended to reflect phylogeny • Primitive characters: • Present in all members of a group, and • Present in the common ancestor • Derived characters: • Present in some members of a group, but • Absent in the common ancestor

  15. Tracing Phylogeny • Fossil Record • Fossil record is incomplete • It is often difficult to determine the phylogeny of a fossil • Homology • Refers to features that stem from a common ancestor • Homologous structures are related to each other through common descent • Analogy • Similarity due to convergence

  16. Ancestral Angiosperm

  17. Tracing Phylogeny • Convergent Evolution • The acquisition of a feature in distantly related lines of descent • The feature is not present in a common ancestor • Parallel Evolution • The acquisition of a feature in two or more related lineages • The feature is not present in a common ancestor

  18. Convergent Evolution

  19. Molecular Data • Protein Comparisons • Immunological techniques • Degree of cross reaction used to judge relationship • Amino acid sequencing • Similar sequence in same protein indicates close relationship • RNA and DNA Comparisons • Systematics assumes: • Two species with similar base-pair sequences are assumed to be closely related • Two species with differing base-pair sequences are assumed to be only distantly related • Molecular Clocks • Use non adaptive nucleotide sequences • Assumed constant rate of mutation over time

  20. Ancestry of Giant Pandas

  21. Molecular Data

  22. Cladistic Systematics • Traces evolutionary history of the group under study • Uses shared derived characters to: • Classify organisms, and • Arrange taxa into a cladogram • A cladogram is a special type of phylogenetic tree • A clade is an evolutionary branch that includes: • A common ancestor, together with • All its descendent species

  23. Constructing a Cladogram

  24. Parsimony • Cladists are always guided by the principle of parsimony • The arrangement requiring the fewest assumptions is preferred • This would: • Leave the fewest number of shared derived characters unexplained • Minimize the number of assumed evolutionary changes • The reliability of a cladogram is dependent on the knowledge and skill of the investigator

  25. Alternate, Simplified Cladograms

  26. Cladistic Versus Traditional View ofReptilian Phylogeny

  27. Phenetic Systematics • Assumes it will never be possible to construct a truly phylogenetic classification system • Species are classified according to the total number of shared similarities • Disregards assumed phylogenetic considerations • Ignores issues of convergent or parallel evolution

  28. Traditional Systematics • Mainly uses anatomical data • Classify organisms using assumed phylogeny with emphasis on phenotype • Stress both common ancestry and degree of structural difference among divergent groups • Construct phylogenetic trees by applying evolutionary principles to categories • Not strict in making sure all taxa are monophyletic

  29. Classification Systems • Until the middle of the twentieth century, biologists recognized only two kingdoms • Plantae (plants) • Animalia (animals) • Protista (protists) were added as third kingdom in the 1880s • Whittaker expanded to five kingdoms in 1969 by adding Fungi and Monera

  30. Three-Domain System • The Bacteria and Archaea are so different they have been assigned to separate domains • Similar in that both are asexually reproducing unicellular prokaryotes • Distinguishable by: • Difference in rRNA base sequences • Plasma membrane chemistry • Cell wall chemistry

  31. Three-Domain System • Domain Eukarya • Unicellular and multicellular organisms • Cells with a membrane-bounded nucleus • Sexual reproduction common • Contains four kingdoms • Kingdom Protista • Kingdom Fungi • Kingdom Plantae • Kingdom Animalia

  32. The Three-DomainSystem of Classification

  33. The Three Domains of Life

  34. Review • Taxonomy • Binomial System • Species Identification • Classification Categories • Phylogenetic Trees • Systematics • Taxonomy (naming of organisms) • Classification (placing species in the proper categories) • Systematics Today • Cladistic Systematics • Phenetic Systematics • Classification Systems • The Five Kingdom System • The Three Domain System