Chapter 20 Classification of Living Things

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Chapter 20 Classification of Living Things
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Taxonomy Science of Classification

• Branch of biology concerned with identifying,
  describing and naming organisms.
• Ideally, classification is based on our
  understanding of how organisms are related to one
  another through evolution
• Not an artificial system

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Taxonomy - History

• Began with Greeks and Romans
• Aristotle - first taxonomic system
• Plants trees, shrubs, and herbs
• Animals air-dwellers, water-dwellers,
  land-dwellers
• System flawed because scientifically valid
  characteristics were often not used in
  determining the categories.

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Carolus Linnaeus (Sweedish botanist)father of
modern taxonomy (1707- 1778)

• Eliminated use of common names
• Used Latin as a basis for nomenclature
• Created "binomial nomenclature" identifying each
  organism by a two-part name

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Linneaus, contd

• Used morphological (form structure)
  characteristics as a basis for classification
• Linnaeus considered each species to have a unique
  structure that made it distinct

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Species name Scientific name

• e.g. Magnolia grandiflora underlined
• Magnolia grandiflora italicized
• genus - Magnolia
• specific epithet - grandiflora
• species - Magnolia grandiflora M. grandiflora

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• Created seven taxa for classification purposes
• Kingdom..most inclusive
• Phylum
• Class
• Order
  Classification Family
  Hierarchy
• Genus
• Species.least inclusive
• Taxon a group of organisms that fills a
  particular category of classification

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Hierarchy of taxa for Callinectes sapidus
Callinectes (Gk. Beautiful swimmer) sapidus (L.
savory)

• Domain Eukarya (Eucaryota)
• Kingdom Animalia
• Phylum Arthropoda
• Class Malacostraca
• Order Decapoda Atlantic Blue Crab
• Family Portunidae
• Genus Callinectes
• Species Callinectes sapidus

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Classification of organisms

• Additional levels of classification can be added
  by adding super-, sub-, or infra- (e.g.,
  sub-order)
• Taxonomists lumpers or splitters

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Classification of organisms

• the higher the classification category, the more
  inclusive it is
• A character is any structural, chromosomal, or
  molecular feature that distinguishes one group
  from another.
• members of a kingdom share general characters
  members of a species share quite specific
  characters

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• The Linnaean system of classification is still
  in use today.
• Linnaeus was devoutly religious, but his
  taxonomic system was later to be used to
  demonstrate the phylogenetic (evolutionary)
  relationships among living organisms.
• Linnaeus Latinized his own name from
• Carl von Linne

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Some points about species

• The biological definition of a species states a
  group of organisms capable of interbreeding and
  producing fertile offspring they share the same
  gene pool.
• Distinguishing species on the basis of
  reproductive isolation can also be a problem.
• Some species do not reproduce sexually.
• Some species hybridize where their geographic
  ranges overlap.
• Reproductive isolation can be difficult to
  observe.
• When a species has a wide geographic range,
  variant types may tend to interbreed where they
  overlap these populations are called subspecies,
  and are designated by a three-part name.

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Genus name may include more than one species or
sub-species
Ursus americanus
Ursus maritimus
Ursus thibetanus
binomial and trinomial
Ursus arctos mittendorfii
Ursus arctos horribilis
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Classification - an ongoing process

• there are estimated to be between 3 and 30
  million species living on earth
• we have currently named one million species of
  animals and a half million plant and
  microorganismic species
• some groups, such as birds, are nearly all known
  some insect groups are mostly unknown 

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Major kingdoms of life

• Work of R.H. Whittaker (1969)
• Five are generally recognized based on
• Cell type
• Organization
• Nutrition

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Five Kingdoms of Life (KEY)

• 1. Cell type
• A. Prokaryotic (P) - primitive, lack
  membrane-bound internal organelles
• B. Eukaryotic (E) - true nucleus, membrane-bound
  organelles
• 2. Cells
• Unicellular (U)
• Colonial (C)
• Multicellular (M)
• 3. Nutrition
• A. Autotrophic (A) - Source of carbon is simple,
  such as carbon dioxide (CO2)
• B. Heterotrophic (H) - Source of carbon is
  complex, such as
• carbohydrates, proteins, lipids, or
  nucleic acids

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Kingdoms of Life

• Many modern taxonomic systems split bacteria
  (Monera) into several different kingdoms.
• Generally,
• protists are considered to have evolved from
  monerans, and
• the fungi, plants, and animals evolved from
  protists via three separate lineages.

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A higher category, the domain, has been proposed
to be added to these 7 categories

• Three-Domain System
• sequencing of rRNA suggests all organisms evolved
  along three distinct lineages domains
• Bacteria
• Archaea
• Eukarya
•      

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Three Domains

• 1. the bacteria diverged first archaea and
  eukarya are more closely related than either is
  to bacteria
•       2. the archaea live in extreme
  environments methanogens in anaerobic swamps,
  halophiles in salt lakes, and thermoacidophiles
  in hot acidic environments
•      the archaea cell wall is diverse but
  not the same as the bacterial cell wall
•       3. the eukarya contains unicellular to
  multicellular organisms, always with a
  membrane-bound nucleus 

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eukarya
archaea
bacteria
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Phylogenetic (Evolutionary) Trees

• Systematics is the study of the diversity of
  organisms using information from cellular to
  population levels
• (Cell, tissue, organ, organism, population)
• A goal of systematics is to determine phylogeny
• Phylogeny is the evolutionary history of a group
  of organisms
• Evolution is a core theme of biology.
• Evolution - the process by which life on earth
  has changed over time.
•      

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Phylogenetic (Evolutionary) Trees

• a phylogenetic tree indicates common ancestors
  and lines of descent or lineages
• an ancestral (primitive) character is a trait
  that is present in a common ancestor and all
  species in its lines of descent
• a derived character is present only in a
  specific line of descent
• Different lineages diverging from a common
  ancestor have ancestral characteristicstraits
  shared by the ancestor and the species in its
  lines of descent.

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Simple phylogenetic tree
(skeletal differences)
(tree climbing)
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All give birth to live young
(placental mammal)
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highly branched
palmate
hollow horns male/female
solid horns (antlers) male only
even-toed hoofs
Classification and Phylogeny
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Tracing Phylogeny

• Systematists use various methods used to discover
  evolutionary relationships between species.
• If you can determine common ancestors, then you
  know how evolution occurred and you can classify
  organisms correctly.

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Fossil Record

•       because fossils can be dated, fossils can
  establish the age of a species
•       most organisms decay and the chances of
  becoming a fossil are low

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Homology morphological data

•       Homology is a character similarity that is
  due to having a common ancestor (anatomical and
  embryological features)
•       homologous structures are related to each
  other through common descent but may differ in
  structure and function (e.g., the forelimbs of a
  horse and the wings of a bat)
•       analogous structures have the same
  function but are not derived from the same organ
  in a common ancestor (e.g., the wings of an
  insect and the wings of a bat)
•       convergent evolution is acquisition of
  similar traits in distantly related lines of
  descent as a result of adaptation to similar
  environmental conditions
•   --both spurges and cacti are adapted to a
  hot, dry environment and are both similar, but
  details of flower structure indicate these two
  groups are not closely related
•       parallel evolution produces similar
  characters in related lineages without occurring
  in a common ancestor

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Molecular Data

•       Speciation (new species) occurs when
  mutations bring about changes in base pair
  sequences of DNA
•       Protein Comparisons
•        earlier studies used immunological
  reactions to antibodies, made by injecting a
  rabbit with cells of one species, to determine
  the relatedness of two species
•        we now use amino acid sequences to
  determine the differences in proteins between two
  species
•        cytochrome c is a protein found in all
  aerobic organisms the amino acid differences in
  cytochrome c between chickens and humans is 13
  but between chickens and ducks is only 3
•        since the number of universal proteins is
  limited, most new studies use differences in RNA
  and DNA.

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RNA and DNA Comparisons

•       all cells have ribosomes for protein
  synthesis comparing rRNA base pair sequences
  provides a reliable indicator of similarity
  between organisms
•       Chimpanzees and Humans
•        DNA DNA hybridization shows chimpanzees
  closer to humans than to other apes
•        yet humans are kept in a separate family
  and chimpanzees are with the ape family due to
  differences in adaptation to the environment
•       Mitochondria DNA (mtDNA) changes ten times
  faster than nuclear DNA
•        mtDNA is often used for closely related
  species

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PhenogramDNA data

• Length of branches
• indicates the relative
• number of nucleotide
• pair differences among
• species shown.

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Molecular Clocks

•       When nucleic acid changes are not tied to
  adaptation - the fairly constant changes provide
  a "molecular clock to indicate relatedness and
  evolutionary time
•       the fossil record can then be used to
  calibrate the clock and confirm the hypothesis
  drawn from molecular data

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Systematics today 3 main schools

• 1. Cladistic Systematics (Willi Hennig)
•       cladistics analyzes primitive and derived
  characters and constructs cladograms on the basis
  of shared derived characters (homologies)
•       cladogram a diagram showing relationships
  among species based on shared, derived characters
•       a clade is an evolutionary branch - that
  includes a common ancestor and all its descendent
  species (monophyletic taxon)
• outgroup - taxon (taxa) that define the
  primitive characters of the study group study
  group taxa placed in a clade
•       Parsimony
•        cladists are guided by principle of
  parsimony the minimum number of assumptions is
  most logical that is, the fewest number of
  shared derived character are left unexplained

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Charcters of taxa being compared
Cladogram w/ 3 clades
monophyletic taxon
Common ancestor notochord in embryo
Notochord- shared ancestral character Others are
shared derived characters
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Systematics today

• 2. Phenetic Systematics
•       phenetic systematists cluster species on
  the basis of the number of shared similarities,
  regardless of whether they might be convergent,
  parallel, or depend on one another
•       results of their analysis are depicted in a
  phenogram
•       phenograms vary for the same group of
  organisms, depending on how the data are
  collected and handled

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Systematics today

• 3. Traditional Systematics
•       traditional systematics stresses common
  ancestry and the degree of structural
  (anatomical) difference among divergent groups in
  order to construct phylogenetic trees
•        a monophyletic group does not include all
  groups from all ancestors (as a clade does)
•       cladists would not use "reptiles" because
  it does not include all organisms derived from
  reptiles

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Traditional vs. cladistic systematics
Hair/ mammary glands
scaly skin
feathers
Traditional view
Cladistic view
Common ancestor-egg layer