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Chapter 18

Biology 1201A Chapter 18: Classification, Evolution, Phylogeny

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Biology 1201A
Richard Gardiner

Chapter 18: Classification, Evolution, Phylogeny 1 18.2 Systematic Biology: An Overview • systematics: 2 goals: 1. reconstruct phylogeny or evolutionary history of group of organisms; presented as phylogenetic trees (formal hypotheses identifying likely relationships among species) - important to analyze evolutionary processes - robust phylogenetic hypotheses: allow to distinguish similarities inherited from common ancestor from those that evolved independently in response to similar environments 2. taxonomy: identification/naming of species & placement in classification - classification: arrangement of organisms into hierarchal groups that reflect relatedness - experiments: first w/ individual of single species, preferably one that is closed genetic system that may respond uniquely to experimental conditions - if researcher used 2 species that responded differently, mixed results would not make sense - selecting species that is androdieocus or gynogenetic=either beneficial or mistake 18.3 Linnaean System of Classification • Carl von Linne (1707-1778): naming/classifying organisms (b/w botanists/zoologists) • taxonomic hierarchy: arrange organisms into categories • family: group of genera that closely resemble one another • orders - > classes - > phyla - > kingdoms • 3 domains, made of taxon - ex. woodpeckers: taxon (Picidae) at family level; pine trees: taxon (Pinus) at genus level • (most inclusive-least inclusive) domain, kingdom, phylum, class, order, family, genus, species 18.4 From Classification to Phylogeny • systematists: relied on organized traits (mainly morphology)- analyzing evolutionary relationships/classifying organisms Chapter 18: Classification, Evolution, Phylogeny 2 • developed phylogenies based on characters, ex. chromosomal anatomy, details of physiological functioning, morphology of sub-cellular structures, cells, organ systems, whole organisms, patterns of behaviour; today- use molecular sequences of nucleic acids & proteins 18.5 Evaluating Systematic Characters • systematists create phylogenetic hypotheses/classifications by analyzing genetic changes that caused speciation & differentiation • fossil record: rely on phenotypic traits; exclude diff. caused by environmental conditions • characters must be genetically independent, reflecting diff. parts of organisms’genomes • homologous characters: sharing same embryological (developmental) history; reflect underlying genetic similarities - > common ancestry, genetic relatedness • homoplasious: phenotypic similarities that evolved independently in different lineages; no info. about shared (genetic) ancestry; ex. flattened tails of aquatic mammals • where function has changed, homologous structures (inherited from common ancestor) can differ considerably among species - ex. bones in wings; (bats, birds, pterosaurs) details of forearm, hand & finger bones differ; considered examples of parallel evolution • mosaic evolution: some characters evolve slowly vs rapidly • every species: ancestral characters (old forms) & derived characters (new forms) - derived - > in relation to what occurs in other organisms, either older version or new trait - most animal species lack vertebrates (fish, amphibians, reptiles, birds); b/c of derived character • out-group comparison: comparing group under study w/ more distantly related species not otherwise inc. in analysis - ex. butterflies: ancestral- 6 walking legs, derived- 4 walking legs & 2 smaller legs 18.6 Phylogenetic Interference & Classification • principle of monophyly: define monophyletic taxa (derived from single ancestral species) • pharaphyletic taxon: inc. ancestor & some, not all, descendants Chapter 18: Classification, Evolution, Phylogeny 3 - ex. Reptilia: obvious- turtles, lizards, dinosaurs; other=mammals, birds • assumption of parsimony: simplest explanation should be most accurate; any particular evolutionary change is an unlikely event & presumably happened only once in evolutionary lineage • phylogenetic tress: organisms on single branch; ex. birds- feathered wings evolved once in common ancestor 18.6a Traditional Evolutionary Systematics Classifies Organisms According to Their Evolutionary History Using Phenotypic Similarities & Differences: • traditional evolutionary systematics: groups together species that share ancestral & derived characters - mammals: internal skeleton, vertebral column, 4 limbs (ancestral) & hair, mammary glands, 4- chambered heart (derived) - classifications produced by traditional systematics reflect evolutionary branching & morphologic
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