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17-1: Biodiversity 17-2: Systematics 17-3: Modern Classification. CHAPTER 17 – CLASSIFICATION OF ORGANiSMS. Biologists have named and classified almost 2 million species
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17-1: Biodiversity 17-2: Systematics 17-3: Modern Classification CHAPTER 17 – CLASSIFICATION OF ORGANiSMS
Biologists have named and classified almost 2millionspecies Over time, scientists have created various systems of classification to organize their knowledge of the tremendous # of species each system places species into categories based on particular characteristics 17-1: Biodiversity
Biodiversity • The variety of organisms considered at all levels from populations to ecosystems • # of ID’d species - increased over time • 100s to millions • Terry Erwin (1980s) • Catalogued insect species in tropical rain forest • Found over 1000 species in only 19 trees • Estimate more than 30 million species on Earth Classifying organisms
Every year, biologists discover 1000s of new species and seek to classify them in a meaningful way • Proposed + modified as scientific understanding increases • Ex. – the pangolin • Grouped with lizards + crocodiles due to scales? • Grouped with animals that use sticky tongues to eat ants? Classifying organisms
Taxonomy • The science of describing, naming, + classifying organisms • Taxon • Any particular group within a taxonomic system • Over time, many different schemes have been developed Taxonomy
Aristotle • Classified organisms in 2 taxa: • Plants • Grouped them based on stemdifferences • Animals • Grouped them based on where they lived: • Land, water, or air Taxonomy
Aristotle’s system was inadequate • Common names were not useful either • Ex. Robin or Fir tree • Vary from place to place • More than one common name • Don’t accurately define a species (i.e. Jellyfish) Taxonomy
Carolus Linnaeus • System that grouped organisms into hierarchicalcategories according to their form + structure(morphology) • System had 7 levels The linnaean system
Kingdom Phylum Class Order Family Genus Species Levels of classification
Linnaeus gave an organism a species name, or scientific name, with two parts: • Genus • Species identifier • Examples: • Homo sapiens • Chaos chaos • Thamnophismelanogaster • Drosophila melanogaster Binomial nomenclature Binomial nomenclature
Kingdom Animalia Phylum Chordata Subphylum Vertebrata Class Mammalia Order Primates Family Hominidae Genus Homo Species sapiens Your classification
Subspecies • Species that live in different geographic areas • Example: • Terrapenecarolinatriungui Binomial nomenclature
Modern biologists consider not only the VISIBLESIMILARITIES but also similarities in: • Embryos • Chromosomes • Proteins • DNA • Systematics • Goal is to classify organisms in terms of their natural relationships • organize in context of evolution 17-2: Systematics
Systematic taxonomists agree that an organism’s classification should reflect PHYLOGENY(evolutionary history) • Phylogenetics • The analysis of the evolutionary or ancestral relationships among taxa. phylogenetics
Use comparisons to classify: • Living species vs. fossils • Embryonic development + gene expression • Chromosomes or macromolecules (DNA/RNA) phylogenetics
Represent hypotheses by a phylogenetic tree (diagram) • Branching pattern indicates how closely related a subset of taxa are thought to be • May be revised with new discoveries or evidence phylogenetics
Biologists use fossils as important clues for the timing of evolutionary changes + divergence • The fossil record my lack evidence… • May also compare… • Homologous features (jaws of pangolin + dogs) • Analogous features (scales of snakes + pangolin) • Embryology (amnion) • The greater the # of features shared by organisms, the more closely related the organisms are Evidence of shared ancestry
1966 – WilliHennig • Cladistics • A system of phylogenetic analysis that uses shared+ derivedcharacters as the only criteria for grouping taxa • Shared– feature that all members of a group have in common • Ex. Hair in mammals or feathers in birds • Derived– feature that evolved only within the group • Ex. Feathers Cladistics
Cladistics assume that organisms share one or more derived characters • Probably inherited them from an common ancestor • Group known as a “clade” • Includes its ancestors + all descendants • No other categories (i.e. order, class, etc..) • Creates a cladogramto show their hypothesis Cladistics
Out-group • Organism that is only distantly related to the other organisms • Acts as a starting point for comparisons Constructing a cladogram
Biologist can count the shared, derived amino acids at each position in a protein to make a cladogram Molecular cladistics
“Molecular Clock” • A tool for estimating the sequence of past evolutionary events • Suggests that the greater the differences between a pair of sequences, the longer ago those two sequences diverged from a common ancestor Molecular cladistics
If two species have the samebandingpattern in regions of similarchromosomes, the regions are likely to have been inherited from a single chromosome in the last common ancestor of the two species chromosomes
To classify an organism and represent its systematics in an evolutionary context, biologists use many types of information to build and revise phylogenetic models: • Physical features • Embryos • Genes in nucleus • Mitochondrial DNA • Ribosomal RNA Putting it all together
Taxonomists have revised two Linnaean-inspired categories • Domains • Kingdoms 17-3: modern classification
Based on cell types, scientists can divide all life into two groups: • Eukaryotes • Prokaryotes • Carl Woese - 1977 • Proposed major revision of 6 kingdom system • Compared rRNA sequences of different organisms and grouped them according to their similarities The tree of life
Insights from rRNA analyses: Data is consistent with hypotheses that all living organisms inherited their rRNA genes from ancient organisms or form of life All living things can be grouped into 1 of the 3 domains: BACTERIA, ARCHAEA, or EUKARYA Species in domain ARCHAEA are greatlydifferent than bacteria Three domains of life
Small, single-celled prokaryotes • Have cell walls • Contain peptidoglycan • Reproduce by binary fission • One circular chromosome Domain bacteria
Have distinctive cell membranes • Made of hydrocarbons, not fatty acids • Some are autotrophic (chemosynthesis) • May inhabit harsh environments Domain archaea
Consists of eukaryotic organisms • Includes plants, animals, fungi, + some single-celled organisms Domain eukarya
The 6 kingdoms are more of a traditional taxonomic system • Kingdoms: • Eubacteria • Archaebacteria • Protista • Fungi • Plantae • Animalia Six kingdoms