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Chapter 25: Phylogeny & Systematics Phylogeny Evolutionary history of species or group of species **Attempting to construct the universal tree of life Information contributing to Phylogenics Fossil record Substantial but incomplete & biased chronicle of evolutionary change Systematics analytical approach to understanding the diversity & relationships of present day & extinct organisms through morphological & biochemical resemblances Systematics Morphological homologies Molecular homologies Similar bone structures indicate species share a common ancestor Similarities in DNA, RNA, & other molecules indicate species share a common ancestor **Potential problems for phylogeny Analogous structures (homoplasies) & convergent evolution Taxonomy Ordered division of organisms into categories based on a set of characteristics used to assess similarities & differences Useful for phylogenic systematics Binomial designations (Genus species) Hierarchical classifications Phylogenetic Trees Depict hypothesis about evolutionary relationships of a species in relative periods of time Cladistics Analysis of how species may be grouped into clades distinguishing analogous from homologous structures Cladogram Depicts patterns of shared characteristics, not necessarily evolutionary history Can be converted to phylogenetic trees with support from fossils, biochemistry, etc. Clade Group of species in the phylogenetic tree that includes an ancestral species & all its descendants Phylogenetic Trees Monophyletic Paraphyletic Clade consists of ancestral species & its descendants Grouping in which information is missing on some members of the clade Polyphyletic Grouping of several species that lack a common ancestor Preparing phylogenetic trees Ingroup Outgroup Novelty trait of a clade Maximum parsimony Trait shared beyond the taxon being defined Shared derived character Species or group of species closely related to ingroup Used to differentiate shared derived & shared primitive characteristics Shared primitive character Species being studied Fewest number of evolutionary events occur to reach form of shared derived characteristics **Nature doesn’t always follow easiest course ex. 4 chamber heart Maximum liklihood Incorporate as much information as possible to reflect the most likely sequence of evolutionary events Evolutionary Diagrams depicting time Phylogram Present information about the sequence of events relative to each other Branch length=# changes in DNA sequence which have occurred in that lineage Ultrametric trees Show sequence of evolutionary events in context of geologic time Molecular Clocks Measures absolute time of evolutionary change based on observations that some genes & other regions of genomes evolve at constant rates DNA coding for rRNA changes relatively slowlyused to study relationships of distantly related species DNA in mitochondria (mtDNA) evolves rapidly – used to study recently diverged species Orthologous genes Homologous genes passed from one generation to the next but end up in different gene pools as a result of speciation Ex. Beta globin genes in humans & mice Paralogous genes Result from gene duplication in one genome Ex. Olfactory genes Universal Tree of Life Tree consists of 3 great domains Bacteria Archaea Eukarya Early history of the domains is not yet clear Molecular systemactics & clocks used to construct