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CH18 Detailed Textbook Notes.docx

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Tristan Long

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Chapter 18: Classification, Evolution, and Phylogeny 18.1 The Significance of Similarities and Differences o Parallel/convergent evolution: tendency among organisms living under the same conditions to develop similar body forms o Convergent: phylogenetially more distantly related organisms o Parallel: closely related ones 18.2 Systemic Biology: An Overview o Science of systematics has 2 major goals: 1. Reconstruct the phylogeny/evolutionary history of an organism 2. Taxonomy a. Identification/naming of species and their placement in classification i. Classification is an arrangement of organisms into hierarchical groups that reflect their relatedness o Closed genetic system means a species not hybridizing with others 18.3 The Linnaean System of Classification o Carl Linnaeus developed a basic system of naming and classifying organisms o Taxonomic hierarchy for arranging organisms into ever more inclusive categories o Family is a group of genera that closely resemble one another o Similar families are grouped into orders, then classes, then phyla, then kingdoms o All life on earth is in 3 domains o Organisms included within any category of the taxonomic hierarchy make up a taxon – or taxa o Domain (Dave, Kindly, Poked, Carla, On, Facebook, the Girl, Said) o Kingdom o Phylum o Class o Order o Family o Genus o Species 18.5 Evaluating Systematic Characters o Systematics create phylogenetic hypothesis and classifications by analyzing the genetic changes that caused speciation and differentiation o Systematics study traits in which phenotypic variation reflects genetic differences o Exclude differences caused by environment o Systematic characters must be genetically different, reflecting different parts of organisms genomes o Different organismal characters can have the same genetic basis o Want to use each genetic variation once in analysis o Homologous characters: sharing the same embryological (developmental) history o Reflect underlying genetic similarities o Common ancestry and genetic relatedness o Emerge from comparable embryonic structures and grow in similar ways during development o Homoplasious: phenotypic similarities that evolved independently in different lineages o Similar functions o Mosaic evolution refers to the reality that in all evolutionary lineages, some characters evolve slow, while others are fast o Pervasive o Every species displays a mix of ancestral characters (old forms) and derived characters (new forms that provide most useful info about evolution relationships) o Systematists score characters as either ancestral or derived only when comparing them among organisms o Any particular character is derived only in relation to what occurs in other organisms o Out-group comparison involves comparing the group under study with more distantly related species not otherwise included in the analysis o -Analogous characters that have the same function o -Phenotypic similarities evolved independently in different linages o Mosaic Evolution- the reality that in all evolutionary lineages, some characters evolve more slowly then others o Every species displays a mixture ancestral and derived characters o Ancestral- old form traits o Derived- new forms of traits (most useful) 18.6 Phylogenetic Inference and Classification o Phylogenetic trees portray the evolutionary diversification of lineages as a hierarchy that reflects the branching pattern of evolution o Each branch represents the descendants of a single ancestral species o Principle monophyly is what systematists use to convert the phylogenetic tree into a classification  They try to define monophyletic taxa, those derived from a single ancestral species o Phylogenetic taxa include species from separate evolutionary lineages o Paraphyletic taxon includes an ancestor and some, but not all of it’s descendants o Assumption of parsimony- the hypotheses that indicate that the fewest amount of mutations is the correct one b/c its unlikely that the same mutation would occur twice in 2 different species o Simplest explanation most likely to be correct o Any particular evolutionary change is assumed to only had happen once in any o Evolutionary lineage 18.6a Traditional Evolutionary Systematics Classifies Organisms According To Their Evolutionary History Using Phenotypic Similarities and Differences o Traditional evolutionary systematics: groups together species that share ancestral and derived characters o Includes evolutionary branching and morphological divergence o Recognizes 4 classes: amphibian, Mammalia, reptilian, and aves (birds)  Given equal ranking because each represents distinct body plan and way of life  Reptilian is a paraphyletic taxon because it includes some descendants of common ancestors, but omits birds and therefore doesn’t include all descendants o Argue that key innovations thought to have initiated adaptive radiation of birds are extreme divergences from the ancestral morphology 18.6b Cladistics Makes Classifications Based on Shared Derived Characters o The Linnaeus’way of practice of using phenotypic similarities (morphological divergence) o Derived and ancestral traits are not simple b/c some species have hair, mammary gland, and a four chambered heart. These are derived characteristics, but some are also ancestral o Cladistics produces phylogenetic hypotheses and classification that reflect only the branching parent of evolution and ignores morphological divergence o Clades: those with similar derived characteristics get grouped together because they have unique characters o Phylogenetic trees produced by cladists (cladograms) illustrate the hypothesized
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