1. 10.4 How to Construct a Cladogram
Unit 10: Speciation
10.4 How to Construct a Cladogram

2. Quick Review
A Cladogram is a diagram that shows how organisms are related based on shared and derived characteristics.
A derived characteristic is one that appears in recent parts of a lineage but not in its older members.
They show a probable evolution of organisms from ancestral groups.
The more closely two organisms are related, the nearer they will be to each other on the tree.

3. How to Read a Cladogram
The diagram below shows a relationship between 4 relatives.
These relatives share a common ancestor at the root of the tree.
Note that this diagram is also a timeline. The older organism is at the bottom of the tree.
Branches on the tree represent speciation.
The four descendants at the top of the tree are different species.

4. How to Read a Cladogram
Species A, B , and C each have characteristics that are unique only to them.
But, they also share some part of their history with species A.
This shared history is the common ancestor.

5. Practice Reading a Cladogram

6. How to Construct a Cladogram
Select the organisms you want to analyze.
For each member of the group, determine some observable traits.
It is good to choose as many traits to examine as possible. This is because not all traits may give reliable or useful answers. Thus, to minimize the chance of error, your analysis should be based on as many traits as possible.
Choose an outgroup-a group of organisms that is evolutionarily older than the organisms you are analyzing.
Usually the outgroup is the one that has no common characteristics-it’s the one that does not match!

7. How to Construct a Cladogram
Construct a matrix-this shows the number of identical characters exhibited by each pair of organisms in your analysis.
Identify the organism most closely related to the outgroup- place it first on the cladogram.
This is the organism that shares the most characters in common.
Place the additional organisms of the tree in order of the most shared characteristics with the outgroup to the least shared characteristics with the outgroup.