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Cladograms and Cladograms and Dichotomous Dichotomous

KeysKeys

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TaxonsTaxons•Most Most generagenera contain a contain a

number of similar speciesnumber of similar species•The genus The genus HomoHomo is an is an

exception (only contains exception (only contains modern humans)modern humans)•Classification is based

on evolutionary evolutionary relationshipsrelationships

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Basis for Modern Basis for Modern TaxonomyTaxonomy•Homologous structuresHomologous structures

(same structure, different (same structure, different function)function)•Similar Similar embryoembryo

developmentdevelopment•Molecular SimilarityMolecular Similarity in in

DNADNA, , RNARNA, or , or amino acidamino acid sequence of Proteinssequence of Proteins

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Homologous Structures (BONES in the FORELIMBS) Homologous Structures (BONES in the FORELIMBS) shows Similarities in mammals.shows Similarities in mammals.

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Similarities in Vertebrate Similarities in Vertebrate EmbryosEmbryos

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CladogramCladogramDiagram showing how organisms are related Diagram showing how organisms are related

based on based on shared, derived characteristicsshared, derived characteristics such as feathers, hair, or scalessuch as feathers, hair, or scales

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Primate Primate CladogramCladogram

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Dichotomous KeyingDichotomous Keying•Used to identify Used to identify

organismsorganisms•Characteristics given in Characteristics given in

pairspairs•Read both Read both

characteristicscharacteristics and and either go to another set either go to another set of characteristics of characteristics OROR identify the organismidentify the organism

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Example of Dichotomous Example of Dichotomous KeyKey

1a Tentacles present – Go to 21a Tentacles present – Go to 21b Tentacles absent – Go to 31b Tentacles absent – Go to 32a Eight Tentacles – Octopus2a Eight Tentacles – Octopus2b More than 8 tentacles – 32b More than 8 tentacles – 33a Tentacles hang down – go to 3a Tentacles hang down – go to 443b Tentacles upright–Sea 3b Tentacles upright–Sea AnemoneAnemone4a Balloon-shaped body–4a Balloon-shaped body–JellyfishJellyfish4b Body NOT balloon-shaped - 54b Body NOT balloon-shaped - 5

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