Chapter 26 Saturday February 13 2016 4 21 PM Chapter 26 Phylogeny and the Tree of Life Classification and Phylogeny Taxonomy grouping species together o Groups taxa based on their similarities and differences subjective o Ex Leopard lion tiger similarities legs tail fur differences patterns vs no pattern Linnaeus s hierarchical classification system is nested o Groups of lower taxa from higher taxa All species in any taxonomy Phylogeny the evolutionary history of a species and its relationship to other species o 26 4 Shown as a tree o 26 5 each branch point rec Which of these is different from the other two o Be able to recognize trees o C is different C and D are sister taxas in A and B o Trees may show time of divergence Based on fossils genetic evidence o Systematics field of study study of phylogenic relationships o To create monophyletic taxa Each taxon includes ancestor and all descendants 26 10 o Paraphyletic taxon off to the side leaves out a common descendant Leaving out uncle joe in group II o Polyphyletic taxon includes species with different ancestors Adding new branch additional branch without common ancestor o Ideally taxonomic level relates to phylogeny 26 4 o Cladistics is a method of determining phylogeny o Must identify homologous because of relationships not recent adaptations characters in a group as ancestral or derived o Create dichotomous trees Based on shared derived characters synapomorphies o Use principle of maximum parsimony to choose best tree Fewest evolutionary events assume that that is the actual thing that happened o Interpreting cladistic trees o Clade all the species on a branch bass including all of its descendants One clade including frog turtle leopard Living in water NOT A CLADE Clip the branch but turtle and leopard falls too o All species in a clade share homologies o o The more shared characters the closer the relationship Can infer the sequence of evolutionary events from cladistic trees but not absolute time Character shared by all earliest Unique character most recent Homologous DNA genes also reveal relationships Will be passed down in descendent species Orthologous genes are inherited from common ancestor Infer more mutations more time since divergence and less closely related Won t be a lot of difference Can go back after deletion and insertion and infer hypothetical sequence when species diverged Molecular based phylogenies can refine or change older trees Can now say which branched off separated first Molecular clocks estimate divergence times Assumes constant rate of neutral homologous DNA mutations over time Calibrated with known fossil ages The Tree of Life Older Five Kingdom System o All placed together in Monera o Cell walls and photosynthetic Plantae o Cell walls and not photosynthetic Fungi Current 3 Domain System The Tree of Life o Last universal common ancestor Common ancestor of eukaryotes and prokaryotes o The root of the tree is complicated by horizontal gene transfer 26 23 On the left ancestor to all life Cells intermingling sharing genetic information Taking DNA and transferring it to another species that it is not related to Horizontal transfers of DNA