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How to construct a Cladogram

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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How to construct a Cladogram

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  1. How to construct a Cladogram

  2. 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.

  3. Vocabulary • Derived Character – has changed compared to the old, or “ancestral”, character. • Cladogram: what scientists call an evolutionary tree.

  4. Example of Cladogram

  5. 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

  6. Example of homology

  7. 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

  8. C B A D E

  9. 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

  10. Data Matrix

  11. 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.

  12. 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.

  13. 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?

  14. Steps to constructing a cladogram • Move the larger pink triangle to the left.

  15. 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.

  16. 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.

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