Modern Classification Techniques

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Modern Classification Techniques
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Taxonomy

• - the science of taxonomy also involves other
  biological sciences such as evolution
• - taxonomy also attempts to determine the
  evolutionary history of groups of organisms
• - scientists compare characteristics of different
  species living today with each other and with
  extinct species
• - there are several different types of evidence
  that scientists can use to classify organisms and
  study evolutionary relationships

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Evidence Used

• (i) radioactive dating
• (ii) comparative anatomy ( Structural Info.)
• (iii) comparative embryology
• (iv) biochemical information ( DNA / Proteins )
• (v) cellular structure
• (vi) behavior

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(i) Radioactive Dating

• fossils are dated either through determining the
  relative age or finding an absolute age.
• relative age - sedimentary rock forms in layers
  so the age of each layer can be determined in
  relation to each other
• the oldest layers are found at the bottom, and
  the younger layers are on top.
• the age of a fossil can be approximated by the
  rocks layer it is found in.

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Absolute Age

• - The absolute age of a fossil or rock can be
  found through radioactive dating.
• A radioactive isotope (atom with additional
  neutrons) breaks down into a new element at a
  known rate called a half-life (a half-life is the
  time it takes for ½ of a radioactive sample to
  break down). Page 113.

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• Carbon Dating Half - life Useful range
• C14 ----------gt C12 5730 yrs 60 000
  yrs
• note for fossils too old for carbon dating, an
  isotope with a longer half - life must be used
• Isotope half - life
• U235 700 million years
• K40 1.25 billion years
• U238 4.5 billion years

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Try This

• Sample Problem
• If you had a fossil with 2 units of C14 left in
  it and you determined that in the living organism
  (or one that is similar) has 16 units of C14, you
  could use one of the following methods to find
  the absolute age of the fossil

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• Method 1
• 1. Determine amount of C14 left in fossil.
• 2. Determine amount of C14 in a living organism
  of the same size and type living today.
• 3. Calculate the number of half-lives needed to
  reduce the C14 in the living organism to the
  amount that is left in the fossil.
• 4. Multiply by the half - life ( in this case,
  5730 years ) to determine the age of the fossil.

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MATH

• Method 2
• N No (½) t/H

• where
• - N units in the fossil
• - No units in the living organism
• - H the half life
• - t time ( this will most likely be the one
  you will be finding)

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(ii) comparative anatomyComparing the anatomy of
organisms indicates a common ancestry because of

• homologous structures - structures having a
  common ancestry but with different uses in
  various species.
• Eg. Similar bone structure of the forelimb of a
  bat, whale, horse and human suggests these
  different species have a similar evolutionary
  origin. Page 113,114 664

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• - analogous structures - body parts of organisms
  that do not have a common evolutionary origin but
  perform similar functions.
• Eg. insect wings and bird wings are similar in
  function but not in structure. Page 665

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• - vestigial organs - small or incomplete organs (
  or bones ) that have no apparent function in one
  organism but do have a function in another
  species. This indicates evolutionary origin from
  a common ancestor. Page 665
• Eg. Human ear muscles, Human appendix, Hip bones
  in whales, Human tail bone, Leg bones in snakes,
  and Forelimbs in the flightless ostrich

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iii) Comparative Embryology

• Comparing the embryos of organisms can indicate a
  common ancestry with other types of living
  organisms because of similar stages of embryonic
  development.
• (eg. gill slits and tail in human embryos
  indicates humans share common ancestry with
  birds, reptiles and fish) Page 665

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(iv) biochemical information ( DNA / Proteins )

• Comparing the biology of one species with another
  at the molecular level (DNA Proteins) can
  indicate a common ancestry. Page 115
• - human proteins (amino acid sequences) have
  more in common with chimpanzee proteins than frog
  proteins.
• - pig or beef insulin is similar enough to
  humans that it can be used to treat human
  diabetes.

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(v) cellular structure

• Studying structures of cells gives clues to their
  evolutionary history.
• - Remember only two basic types of cells
  prokaryotic and eukaryotic (review p. 106)
• - fossil evidence has shown the first life forms
  were prokaryotic (similar in appearance to
  bacteria) and existed approximately 3.5 billion
  years ago
• -eukaryotes appeared only about 1.5 billion years
  ago
• - multicellular organisms only 700 million years
  ago

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(vi) behavior

• how organisms are adapted in how they respond to
  their environment is called behavioral
  adaptations
• eg. include migration, courtship displays,
  foraging behavior
• - it is believed that these adaptations have
  evolved in response to changes in environmental
  conditions as continents formed and moved
  millions of years ago
• - the favorable adaptations were passed on to the
  offspring
• - note Biofact p.706

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• How have classification systems improved as a
  result of these modern techniques?
• - through the use of these techniques, organisms
  once thought to be closely related, have been
  found not to be related and vise versa.

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Phylogeny and Cladistics
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Phylogeny and Phylogenetic Tree

• A hypotheses about the evolutionary history of an
  organism.
• The roots of the phylogenetic tree show the
  oldest ancestral species.
• The upper ends of the branches show current
  species.
• Each fork represents the adaptation that changed
  the common species into two new species.
• Use the example on page 116.

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Cladistics

• Cladistics is a classification scheme based on
  phylogeny.
• A Cladogram is similar in design to the
  phylogenetic tree, but used to test hypotheses
  about how the branches could have occurred.
• Which of the following 3 cladograms makes the
  most sense.

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Homework

• PAGE 121
• 1, 2, 5,6, 9 (paragraph), and 12