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Classification. Ch 20. 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)

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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

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