Chapter%2018:%20The%20Tree%20Of%20Life

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Chapter 18 The Tree Of Life
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The Linnaean System of Classification

• Words to Know Taxonomy, Taxon, Binomial
  Nomenclature, Genus, species

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Linnaeus

• Swedish botanist Carolus Linnaeus introduced a
  scientific naming system in the 1750s.
• Before that time, naturalists could not talk
  about what they had discovered because there was
  no universal naming system.

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Taxonomy

• Taxonomy is the science of naming and classifying
  organisms.
• This gave scientists a standard way to refer to
  species and organize the diversity of living
  things.
• Linnaeuss system classifies organisms based on
  their physical hierarchy.
• A group of organisms in a classification system
  is called a taxon (taxa)
• The basic taxon in the Linnaean system is the
  species.

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Taxonomy

• From broadest to most specific Linnaeans
  Taxonomy is
• Kingdom King Broadest
• Phylum Phillip
• Class Came
• Order Over
• Family From
• Genus Germany
• Species Sunday Most Specific

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Scientific Names

• Binomial Nomenclature is a system that gives each
  species a two-part scientific name using Latin
  words.
• The first part of the name is the Genus and the
  second name is the Species.
• The Genus is always CAPITALIZED and the species
  is lowercase.
• Binomial Nomenclature is ALWAYS written in
  Italics or Underlined.
• Ex Quercus alba (white oak tree) and Puma
  concolor (mountain lion)

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The Linnaean Classification System has Limitations

• Linnaeus created his classification system BEFORE
  technology allowed us to study organisms on the
  molecular level.
• Linnaeus system does not account for
  similarities that evolved this way.
• Scientists now use genetic research to help
  classify living things.
• Ex The Giant Panda and Raccoon have been placed
  in the same family in the Linnaean system BUT the
  Panda is more closely related to bears
  genetically than raccoons.
• The Red Panda is actually more closely related to
  the raccoon.

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Classification Based on Evolutionary Relationships

• Words to Know Phylogeny, Cladistics, Cladogram,
  Derived Characteristics, taxon

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Phylogeny

• To classify species according to how they are
  related, scientists must look at more than just
  physical traits.
• Modern classification is based on evolutionary
  relationships.
• The evolutionary history of a group of species is
  called a Phylogeny.
• Phylogenics can be shown as branching tree
  diagrams.

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Cladistics

• The most common method used to make evolutionary
  trees is called cladistics.
• Cladistics is classification based on common
  ancestry.
• A Cladogram is an evolutionary tree that proposes
  how species may be related to each other through
  common ancestors.
• The traits that can be used to figure out
  evolutionary relationships among a group of
  species are those that are shared by some species
  but are not present in others.
• These traits are called Derived Characteristics.

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Cladogram
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Interpreting a Cladogram

• In a cladogram, groups of species are placed in
  order by the derived characters that have added
  up in their lineage over time
• Each place where a branch splits is called a
  node.
• Nodes represent the most recent common ancestor
  shared by a clade.
• You can identify clades by using the snip rule.
• Whenever you snip a branch under a node, a
  clade falls off.
• Ex Tetrapod Cladogram
• All organisms in this clade have the derived
  character of 4 limbs.
• Embryo protected by amniotic fluid show where
  mammals branch off.
• Skull openings lead to turtles
• By the time you get to birds, they have every
  characteristic that comes before them.

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Species Relatedness

• Today, new technology allows biologists to
  compare groups of species at the molecular level.
• In many cases, molecular data agree with
  classification based on physical similarities.
• Ex Based on physical traits, most biologists
  considered segmented worms and arthropods to be
  more closely related than other species.
• Through molecular comparisons they discovered
  that round worms, NOT segmented worms should be
  more closely related to arthropods.

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Molecular Clocks

• Words to Know Molecular Clock, Mitochondrial
  DNA, Ribosomal RNA.

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Molecular Clocks

• In the early 1960s, biochemists Linus Pauling
  and Emile Zuckerkandl proposed a new way to
  measure evolutionary time.
• They compare amino acid sequences of hemoglobin
  to determine ancestry.

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Molecular Evolution

• Molecular Clocks are models that use mutation
  rates to measure evolutionary time.
• Pauling and Zuckerkandl found that mutations tend
  to add up at a constant rate for a group of
  related species.
• The more time that has passed since two species
  have diverged from a common ancestor, the more
  mutations will have built up in each lineage, and
  the more different the two species will be at the
  molecular level.

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Linking Molecular Data with Real Time

• To estimate mutation rates, scientists must find
  links between molecular data and real time.
• If scientists know when the species began to
  diverge from a common ancestor, they can find the
  mutation rate fro the molecule they are studying.
• Links can also come from fossil evidence.

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Mitochondrial DNA and Ribosomal RNA.

• Mitochondrial DNA is DNA found only in
  mitochondria, the energy factories of cells.
• The mutation rate of mtDNA is about ten times
  faster than that of nuclear DNA, which makes
  mtDNA a good molecular clock for closely related
  species.
• It is ALWAYS inherited from the MOTHER of
  mitochondria in a sperm cell and are lost after
  fertilization.
• This helps trace cells back many generations.
• Ribosomal RNA is useful for studying distantly
  related species, such as species that are in
  different kingdoms or phyla.
• Mutations in Ribosomal RNA are at a much slower
  rate.

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Domains and Kingdoms

• Words to Know Bacteria, Archaea, Eukarya,
  prokaryote, eukaryote

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Classification is Always a Work in Progress

• 1753 classification has 2 kingdoms plantae
  and animalia
• 1866 classification has 3 kingdoms protista,
  plantae, animalia.
• 1938 classification has 4 kingdoms monera,
  protista, plantae, animalia.
• 1959 classification has 5 kingdoms monera,
  protista, fungi, plantae, animalia
• 1977 classification has 6 kingdoms archae,
  bacteria, protista, fungi, plantae, animalia
• Now Domains broader than kingdoms archae,
  bacteria, eukarya

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The Three Domains

• The Three Domains are Bacteria, Archaea, and
  Eukarya
• Bacteria
• The domain Bacteria includes single-celled
  prokaryotes in the kingdom Eubacteria.
• Eubacteria can be classified by many traits, such
  as their shape, need for oxygen, and whether they
  cause disease.

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Archaea

• The domain Archaea are single-celled prokaryotes.
• However, the cell walls of archaea and bacteria
  are chemically different.
• Archaeabacteria can live in Extreme environments
  such as deep sea vents, hot geysers, Antarctic
  water, and salt lakes.
• All archaea are classified in the kingdom
  Archaeabacteria.

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Eukarya

• The domain Eukarya is made up of all organisms
  with eukaryotic cells.
• Eukaryotic cells have a distinct nucleus and
  membrane-bound organelles.
• They can be single-celled, colonial, or
  multicellular.
• The domain Eukarya includes the kingdoms
  Protista, Fungi, Plantae and Animalia

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Classifying Bacteria and Archae

• Some scientists think that Bacteria and Archaea
  have NO true species.
• This is because many of these organisms transfer
  genes among themselves outside of typical
  reproduction.
• Our understanding of classifying bacteria is
  truly just beginning.