BB 3140 Evolution Term B 2009 chapter 2

BB 3140 Evolution Term B 2009 chapter 2 - BB 3140 Evolution...

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BB 3140 Evolution Term B 2009 Course Outline Chapter 2 Classification and Phylogeny I. Classification according to Linnaeus A. Carolus Linnaeus, Systema Naturae 1735 B. Classification scheme for all species 1. Binomial nomenclature a. Genus name (uppercase) species name (lower case) b. Italicized c. Example: Homo sapiens d. Species names are unique e. Priority given to the name first assigned 2. Hierarchical classification scheme a. Nested scheme: lower levels are nested within higher levels b. Levels (categories) are as follows: i. Kingdom ii. Phylum iii. Class iv. Order v. Family vi. Genus vii. Species viii. Variety c. Taxa are particular groups of organisms that are assigned to one of these categories 3. Basis for assigning taxa to categories II. Modern classification is based on evolution as well as similarity A. Phylogeny: Estimation of the true history of evolution ("Family tree", Fig. 2.1, 2.2 ) 1. Cladogenesis-- splitting or branching of a lineage into two or more descendent lines 2. Anagenesis-- change in characteristics within a lineage 3. Homologous feature-- similar in two different species because it was inherited from the organisms's common ancestor 4. Monophyletic group-- a group of taxa containing a common ancestor and all of its descendents 5. Polyphyletic group-- group of taxa placed together by similarities, but more closely related to other species not placed in 7
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the group (example: if whales and sharks were placed together, they would constitute a polyphyletic group) 6. Paraphyletic group-- monophyletic group from which some descendents have been removed (example: orangutans and chimps traditionally grouped separately from humans even though humans and chimps are believed to share a more recent common ancestor than chimp and orangutans) C. Phenetics-- version of numerical taxonomy. Sokal and Michener 1950's 1. Base classification on overall similarity, not just "important" features selected based on subjective criteria 2. Phenogram: a diagram of similarities among species 3. Character: a feature that varies independently of other features and is homologous among the taxa of interest 4. Character state: one of the alternative conditions of the character a. e.g., presence vs absence of a feature 5. Method (Fig. 2.5A) a. List character states for all available characters for each taxon b. Tally (sum) how many character states each pair of taxa shares in common c. Join pair of taxa with the most shared character states by a line as the "most similar" species d. Decide which of the other species is most similar to the first pair, etc. D. Classification based on similarity does not necessarily provide an accurate phylogeny: Of three reasons why a character state might be similar in two species, two of them are misleading 1. Two species share a derived character state that evolved in their common ancestor (this one is useful for phylogeny! Fig. 2.6 )
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