presentation_6 - Lecture 6 Phylogenetics I Systematic...

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Unformatted text preview: Lecture 6 Phylogenetics I Systematic biology Systematics is the scientific study of the kinds and diversity of organisms and of any and all relationships among themTaxonomy is the theory and practice of classifying organisms. (Ernst Mayr 1942) Goals of modern systematics Identification & Classification: To establish the basic units (species and higher categories) and to arrange these in a logical order. Variation is not continuous - appears to come in discrete units (species) Nomenclature: To apply distinctive names. Phylogeny reconstruction: To determine the evolutionary relationships among species and groups of species. Classification Nomenclature Passer domesticus Passer montanus Phylogenies are simply extended pedigrees, reflecting descent with modification Individuals within a single sexually reproducing population Populations become isolated and different modifications appear in each. A B C D E F G Extant taxa are the result of a history of descent with modification. 1 2 3 MRCA 1 2 3 Green circles are ancestors of the current species. Red and blue tick marks represent modifications that occurred during the history of descent. The red modifications are shared by all three species, whereas blue modifications are shared by species 1 and 2 only. MRCA = most recent common ancestor Descent with modification leads to hierarchy in patterns of variation Hierarchy in patterns of variation We recognize series of hierarchical categories (rank or level in a classification). At each level have different taxa- group of organisms sufficiently distinct from other groups to warrant a name. Passer domesticus Passer montanus Passerella illiaca Passerina cyanae Genus 1 Genus 2 Genus 3 Family 1 Family 2 Passerina amoena Chimpanzee Gorilla Orangutan Human Relatives Family Hylobatidae (Gibbons) Family Hominidae (Great Apes and Humans) Hylobates Ponginae Pongo Homininae Gorilla Homo Humans and close relatives Hierarchy of categories Kingdom/Domain Phylum Class Order Family Genus Species Formal studies of variation must be based on...
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presentation_6 - Lecture 6 Phylogenetics I Systematic...

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