26_Lecture_Post - Phylogeny and the Tree of Life Overview:...

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Phylogeny and the Tree of Life Overview: Investigating the Tree of Life Legless lizards have evolved independently in several different groups Phylogeny is the evolutionary history of a species or group of related species
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The discipline of systematics classifies organisms and determines their evolutionary relationships Systematists use fossil, molecular, and genetic data to infer evolutionary relationships
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Phylogenies show evolutionary relationships Taxonomy is the ordered division and naming of organisms Binomial nomenclature In the 18th century, Carolus Linnaeus published a system of taxonomy based on resemblances Two key features of his system remain useful today: two-part names for species and hierarchical classification
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The two-part scientific name of a species is called a binomial The first part of the name is the genus The second part, called the specific epithet , is unique for each species within the genus The first letter of the genus is capitalized, and the entire species name is italicized Both parts together name the species (not the specific epithet alone)
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Hierarchical Classification Linnaeus introduced a system for grouping species in increasingly broad categories The taxonomic groups from broad to narrow are domain , kingdom , phylum , class , order , family , genus, and species A taxonomic unit at any level of hierarchy is called a taxon The broader taxa are not comparable between lineages For example, an order of snails has less genetic diversity than an order of mammals
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Figure 26.3 Species: Panthera pardus Genus: Panthera Family: Felidae Order: Carnivora Class: Mammalia Phylum: Chordata Domain: Bacteria Kingdom: Animalia Domain: Archaea Domain: Eukarya
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Figure 26.4 – The connection between classification and phylogeny Order Family Panthera pardus (leopard) Genus Species Canis latrans (coyote) Taxidea taxus (American badger) Lutra lutra (European otter) Canis lupus (gray wolf) Felidae Carnivora Panthera Taxidea Mustelidae Lutra Canidae Canis
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Linnaean classification and phylogeny can differ from each other Systematists have proposed the PhyloCode , which recognizes only groups that include a common ancestor and all its descendents A phylogenetic tree represents a hypothesis about evolutionary relationships Each branch point represents the divergence of two species Sister taxa are groups that share an immediate common ancestor
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A rooted tree includes a branch to represent the last common ancestor of all taxa in the tree A basal taxon diverges early in the history of a group and originates near the common ancestor of the group A polytomy is a branch from which more than two groups emerge
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What We Can and Cannot Learn from Phylogenetic Trees Phylogenetic trees show patterns of descent, NOT phenotypic similarity Phylogenetic trees DO NOT indicate when species evolved or how much change occurred in a lineage It SHOULD NOT be assumed that a taxon evolved from the taxon next to it
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This note was uploaded on 04/30/2011 for the course BIOL 1362 taught by Professor Loeblich during the Spring '08 term at University of Houston.

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26_Lecture_Post - Phylogeny and the Tree of Life Overview:...

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