LSU BIOL 1002 - Systematics: Seeking Order Amidst Diversity

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Chapter 1818.1 How Are Organisms Named and Classified?Slide 3Three Species of BluebirdSlide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Human and Chimp Chromosomes Are Very Similar18.2 What Are the Domains of Life?Slide 14Slide 15The Tree of LifeSlide 1718.3 Why Do Classifications Change?18.4 How Many Species Exist?Slide 20Slide 21Chapter 18 Systematics: Seeking Order Amidst Diversity18.1 How Are Organisms Named and Classified? •The branch of biology that is concerned with naming and classifying organisms is known as taxonomy •Modern taxonomy was established by the Swedish naturalist Carolus Linnaeus •Linnaeus introduced the two-part scientific name to all organisms•The two-part scientific name of an organism is formed from the genus and species –A genus is a group that includes a number of very closely related species –A species within a genus includes populations of organisms that can potentially interbreed under natural conditions •The genus Sialia (bluebirds) includes three species –Sialia sialis (the eastern bluebird) –Sialia mexicana (the western bluebird) –Sialia currucoides (the mountain bluebird)Three Species of Bluebird Fig. 18-1•Scientific names are always underlined or italicized –The first letter of the genus name is always capitalized –The first letter of the species name is always lowercase •The species name is always paired with its genus name•The Linnaean classification system includes eight major taxonomic categories, each category including all the categories beneath it. Domain  Kingdom  Phylum  Class  Order  Family  Genus  Species•Modern classification emphasizes patterns of evolutionary descent as biologists realized that taxonomic categories should reflect evolutionary relatedness •The more categories two organisms share, the closer their evolutionary relationship–Today, the process of classification focuses on reconstructing phylogeny, or evolutionary history –The science of reconstructing phylogeny is known as systematics•Systematists identify features that reveal evolutionary relationships –All organisms share certain similarities –Biologists look at many kinds of characteristics in the search for informative similarities•Anatomy plays a key role in systematics –Systematists look carefully at similarities in both external body structure and internal structures, such as skeletons and muscles –Homologous structures such as the finger bones of dolphins, bats, seals, and humans provide evidence of a common ancestor•Molecular similarities are also useful for reconstructing phylogeny –Systematists examine genetic similarities between DNA nucleotide sequences •It has been estimated that 96% of the chimpanzee genome is identical with that of humans –Similarities in actual chromosome structure also can be used to establish relationships between organisms1 2 3 4 5 6 7 X8 9 10 11 12 13 14 1516 17 18 19 20 21 22YHCHCHCHCHCHCHCHCHCHCHCHCHCHCHCHCHCHCHCHCHCHCHCHCHuman and Chimp Chromosomes Are Very Similar Fig. 18-418.2 What Are the Domains of Life? •Before 1970, systematists divided all species into two groups •Animalia •Plantae (including plants, bacteria, fungi, and photosynthetic eukaryotes) •As knowledge expanded of life’s evolutionary relationships, it became clear that a two-domain approach was an oversimplification•A three-domain system more accurately reflects life’s history –Carl Woese discovered that prokaryotic organisms included two very distinct groups (Bacteria and Archaea)•Our current three-domain system: •Bacteria (prokaryotic) •Archaea (prokaryotic) •Eukarya (eukaryotic) –These three split very early in life, long before animals and plants evolvedThe Tree of Life Fig. 18-6BACTERIA ARCHAEA EUKARYAfungiplantsanimalsprotists–Within the domain Eukarya, there are four different groups of organisms (Kingdoms): •Animalia (animals) •Plantae (plants)•Fungi (fungi) •Protists (eukaryotic organisms that are not animals, plants or fungi)18.3 Why Do Classifications Change? •Science is a PROCESS, not a list of facts. Classifications change when new information is discovered –Changes at the Domain and Kingdom level are rare, but there are frequent changes in species level –It was previously thought that there were only two species of elephant, African and Indian •More recently, the African elephant species has been divided into two species—the savannah elephant and the forest elephant •Genetically, these two African species have no more in common than lions and tigers18.4 How Many Species Exist? •Biodiversity is the total number of species in an ecosystem –The number of named species is currently about 1.5 million (biased toward large organisms in temperate regions) •5% are prokaryotes and protists •22% are plants and fungi •73% are animals•It is estimated that 7 million to 10 million species may exist •Between 7,000 and 10,000 new species are identified every year. •Tropical rainforests are believed to be home to two-thirds of the world’s existing species, most of which have yet to be named•Because tropical rainforests are being destroyed so rapidly, species may become extinct before we even know they exist •The unexplored continent of the deep-sea floor may have hundreds of thousands of unknown species to be


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LSU BIOL 1002 - Systematics: Seeking Order Amidst Diversity

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