EVERGREEN INS 2008 - Methods of classifying organisms

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Some things you should know before going home tonight . . .There are ancient “things” jumping around in your genomeand there are dinosaurs are in your backyard!Constructing Trees 101Methods of classifying organismsPheneticsandCladisticsPlacement of Cetaceans• Morphology of astragalus unites Artiodactyls• Most parsimonius placement = one gain of pulley-shaped astralagusPlacement of Cetaceans• DNA evidence suggest Hippos have shared genes with Cetaceans more recently than they have with other Artiodactyls (e.g. deer)Which Tree Best Represents the Evolutionary History of the Hippo?The parsimonious one based on the gain of pulley-shaped astralagusorThe tree based on DNA evidence?MORE WORK NEEDS TO DONE!SINES. . . (hey, what are those?)Genomic Repetitive ElementsThey are in your genome. . . They jump around . . . They make more of themselves. . .They “sleep”. . .sometimesThey can be useful for identifying relationshipsPlacement of Cetaceans• Look at presence/absence of SINE’s throughout genome – Selectively neutral– Once established, loss is random & requires manygenerationsPlacement of CetaceansThis new data further supports this hypothesis (tree).Example #2Grouping based on similarities (phenetics)vsPhylogenetic classification system (cladistics)Imagine what a tree would look like with these organisms:Turtles, lizards, snakes, non-avian dinosaurs, crocodiles and birdsPhylogenetic Classification SystemDid your tree look like this?names only clades (aka; monophyletic group, lineages) — groups of organisms that are all descended from a common ancestorWe could name any clade on this tree . . . For example, the Testudines, Squamata, Archosauria, and Crocodylomorpha all form clades.However, reptiles do not form a clade. . . That means that either “reptile” is not a valid phylogenetic grouping or we have to start thinking of birds as reptilesAnother cool thing about phylogenetic classification is that it means that dinosaurs are not entirely extinct. Birds are, in fact, dinosaurs!(part of the clade Dinosauria)OK, let’s practice . . .From studying fossils and lineages closely related to the vertebrate clade, we hypothesize that the ancestor of vertebrates had none of these features:A -B -G -C -D -E -F -Amniotic egg:Egg in which the embryo is surrounded by the moisture-retaining amnion membranePost-orbital fenestrae:Holes in the skull behind the eyeLet’s draw a tree from the data! Start with the ancestor. . . then make two groups. . .then make new groupsA -B -G -C -D -E -F -Draw lines to indicate the derived character A -B -G -C -D -E -F -Carry on . . .work with a partner to finish the tree.A -B -G -C -D -E -F -Does your tree look like


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EVERGREEN INS 2008 - Methods of classifying organisms

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