How to Build a Cladogram.
Background:
TOC#
Cladograms are diagrams that we use to show phylogenies. A phylogeny is a hypothesized evolutionary
history
... [Show More] between species that takes into account things such as physical traits, biochemical traits, and fossil
records. To build a cladogram one must take into account all of these traits and compare them among
organisms.
Building a cladogram can seem challenging at first, but following a few simple steps can be very
beneficial. Watch the following, short video, read the directions, and then practice building some cladograms.
Video: http://ccl.northwestern.edu/simevolution/obonu/cladograms/Open-This-File.swf
Instructions:
There are two steps that will help you build a cladogram.
Step One “The Chart”:
1. First, you need to make a “characteristics chart” the helps you analyze which characteristics
each specieshas. Fill in a “x” for yes it has the trait and “o” for “no” for each of the
organisms below.
2. Then you count how many times you wrote yes for each characteristic. Those
characteristics with a large number of “yeses” are more ancestral characteristics because they
are shared by many. Those traits with fewer yeses, are shared derived characters, or derived
characters and have evolved later.
Chart Example:
Backbone Legs Hair
Earthworm O O O
Fish X O O
Lizard X X O
Human X X X
“yes count” 3 2 1
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Step Two “The Venn Diagram”: This step will help you to learn to build Cladograms, but once you
figure it out, you may not always need to do this step.
1. Draw a multi-cicular Venn diagram. You will need as many circles as there are characters.
2. Start with the character that is shared by all the taxa on the outside. (you will want to make
this a large circle.)
3. Inside each box, write the species that have only that set of characters.
4. On the outside of the Venn Diagram, write the outgroup. This is a group of organisms that do not
share any traits and serve as a comparison to the phylogeny you are looking at.
Hair: human
Legs: lizard
Backbone: fish
Outgroup: Earthworm
Step Three “The Cladogram”:
This step converts the Venn Diagram into a cladogram. The traits are written on the main line,
and species go on the branches. On the cladogram below, try to put all the characters and the species in [Show Less]