How to construct a Cladogram

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How to construct a Cladogram
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Vocabulary

• Character an attribute the organism has.
• A typical character for an animals might be
  eye color.
• For plants, it might be petal number.
• Character state one of two or more forms of a
  character.
• Animals might have "red" or "black" eyes.

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Vocabulary

• Derived Character has changed compared to the
  old, or ancestral, character.
• Cladogram what scientists call an evolutionary
  tree.

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Example of Cladogram
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Vocabulary

• Evolution- descent with modification
• Homology- similarity between structures due to
  common ancestory.
• Ex. Bat wing and human arm
• Speciation When a single species splits into
  two species. Usually as the result of a new
  character state developing

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Example of homology
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Constructing a cladogram

• You have received a bag with 5 critters.
• First we need to identify the critters.
• What is the system that scientists use to
  identify and name new organisms?
• Lets use letters to identify the shapes

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C
B
A
D
E
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Constructing a Data Matrix

• Need to assign characters and character
  states to describe the structures found on the
  organisms.
• Example
• Character Color
• Character States for Color Pink
• 
  Blue
• 
  Red

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Data Matrix
Name Color Character Character Character
A Blue      
B Blue      
C Pink      
D Red      
E Red      
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How to construct a cladogram

• Remember that evolutionary changes are rare, and
  tend to occur only once.
• One character in our data matrix is
  uninformative. Which one is it?
• We need to know what the common ancestor of your
  geometric shape looked like.
• The ancestor is small relative to the other
  shapes.

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Steps to constructing a cladogram

• Place all the geometric shapes on your desk.
• Place the ancestor at the bottom of your desk
  and put the other shapes at the top of your desk.
• Draw imaginary lines from the ancestor to the
  other shapes.

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Steps to constructing a cladogram

• Determine which of the critters require the LEAST
  NUMBER of steps to change from the ancestors.
• Which critter should we chose?
• Why?

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Steps to constructing a cladogram

• Move the larger pink triangle to the left.

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Steps to constructing a cladogram

• Can you finish the cladogram with the geometric
  objects, showing the derived characters in each
  step?
• Use the post-it notes provided to write out the
  derived characters.

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The new critters

• Working in pairs you need to create a cladogram
  for the newly discovered critters.
• The hypothetical ancestor had hooves (the dark
  appendages) and a short neck.
• Suggestion start with neck length.