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Modern Classification Techniques by rsnRgbG5


									Modern Classification
   - 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
             Evidence Used

(i) radioactive dating
(ii) comparative anatomy ( Structural Info.)
(iii) comparative embryology
(iv) biochemical information ( DNA / Proteins )
(v) cellular structure
(vi) behavior
        (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
 the age of a fossil can be approximated
  by the rocks layer it is found in.
              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
Carbon Dating              Half - life Useful range
C14 ----------> 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
                   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:
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.
Method 2:               where:
 N = No (½) t/H        - N = units in the fossil
  2 = 16 (½)t/5730      - No = units in the
                          living organism
  1/8 = (½)t/5730
                        - H = the half – life
  (½)3 = (½)t/5730      - t = time ( this will
                          most likely be the one
  3 = t/5730
                          you will be finding)
t = 3 x 5730
         (ii) comparative anatomy
Comparing 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
   - analogous structures - body parts of
    organisms that do not have a common
    evolutionary origin but perform similar
      Eg. insect wings and bird wings are
       similar in function but not in structure.
       Page 665
- 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
     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
      (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
 - 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.
              (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
                     (vi) behavior
-   how organisms are adapted in how they respond
    to their environment is called behavioral
    -   eg. include migration, courtship displays, foraging
- 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
- note: Biofact p.706
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.
Phylogeny and Cladistics
    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.

   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.

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

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