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. Animals might have "red" or "black" eyes.

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

Example of Cladogram

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

Example of homology

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

C A B D E

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

Data Matrix Name Color Character A Blue   B C Pink D Red E

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 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 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 cladogram Move the larger pink triangle to the left.

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 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.