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How to construct a Cladogram

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How to construct a Cladogram. 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.

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vocabulary
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.

vocabulary1
Vocabulary
  • Derived Character – has changed compared to the old, or “ancestral”, character.
  • Cladogram: what scientists call an evolutionary tree.
vocabulary2
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
constructing a cladogram
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?
  • Let’s use letters to identify the shapes
slide8

C

B

A

D

E

constructing a data matrix
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

how to construct a cladogram1
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.
steps to constructing a cladogram
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.
steps to constructing a cladogram1
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?
steps to constructing a cladogram2
Steps to constructing a cladogram
  • Move the larger pink triangle to the left.
steps to constructing a cladogram3
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.
the new critters
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.