Making Cladogramsi
Purpose: To make a cladogram and use it to show common ancestry and evolutionary
relationships between certain organisms.
Background: One way to discover how groups of organisms are related to each other is
to compare their body organs and parts. Body organs and parts that are similar in basic
structure and origin (like the arm bones of a horse, bird, whale and human) are called
homologous structures. When organisms share a large number of homologous structures,
it is considered strong evidence that they are related to each other. When organisms are
related to each other, it means they must have had a common ancestor at some time in the
past. If there are specific changes in the features shared by different groups of organisms,
we call those features “shared derived characteristics”.
When we do studies that look at the different numbers of shared derived characteristics
between organisms we can draw a diagram of branching lines that connect these groups
of organisms. These diagrams look like trees and are called cladograms. Cladograms
allow us to see relationships between groups of organisms by looking at how many
derived characteristics they share as shown by the branches in the tree.
When making a cladogram, the organisms are at the tips of the branch stems. The shared
derived characteristics are shown by solid square boxes along the branches and the
common ancestors are shown by open circles. Look at figure 1 below for an example.
The more derived characteristics two organisms share, the closer their evolutionary
relationship is—that is, their common ancestor lived more recently. On the cladogram,
close relationships are shown by a recent fork from the supporting branch. The closer the
fork in the branch between two organisms, the closer is their relationship.
Figure 1: Example of a Cladogram
Pre-lab questions:
1. What does it mean when two organisms are related to each other?
2. How can we use a cladogram to tell if two organisms are related to each other?
3. What are shared derived characteristics? Do related organisms have more or
fewer shared derived characters?
Procedure:
1. Review data table 1 to see which characteristics each organism has. An “X” has
been placed in the box if the organism has the characteristic . The characteristics
are explained in appendix A at the end of the lab.
2. Use the data table to make a Venn diagram, placing the animals in groups to
illustrate the characteristics that the different organisms have in common. See the
figure 2 below for an example.
Figure 2: Example of Venn diagram
3. Using the Venn diagrams of the groupings just completed, draw a cladogram on
the larger sheet of paper to illustrate the ancestry and relationships of these
animals. The diagram should reflect shared derived characteristics as time
continues. Look back at figure 1 for an example. Notice how the different
animals are all at the same time level (across the top) since they all live today.
Analysis questions
1. What are at least two types of information that a scientist can get by using a
cladogram?
a.
b.
2. A scientist wants to add three more organisms to this cladogram. Between which
other organisms would she put them and why?
a. “Iguana-like” animal:
b. “Rat-like” animal:
c. “Goldfish- like” animal:
Data Table 1: Various Animals and the Characteristics They Have
Traits
Animals
Kangaroo
Lamprey
Rhesus
Monkey
Bullfrog
Human
Snapping
Turtle
Dorsal Nerve Cord
Notochord
X
X
X
X
X
X
X
Paired Appendages
Vertebral column
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Paired Legs
Amnion
Mammary Glands
Placenta
Canine teeth short
Foramen magnum fwd
Total # of X's
Venn Diagram:
X
Tuna
Appendix A: Explanation of Characteristics
Characteristic
Explanation
Dorsal Nerve Cord
nerve cord running along the back of the body surface
Notochord
a flexible but supporting rod running along the back of the body
surface
Paired Appendages
legs, arms, wings, fins, flippers, antennae
Vertebral Column
“backbone”
Paired Legs
legs in pairs
Amnion
membrane that holds the amniotic fluid surrounding the embryo;
may or may not be inside an egg shell
Mammary Glands
milk-secreting glands that nourish the young
Placenta
structure attached to inside of uterus of mother, and joined to the
embryo by the umbilical cord; provides nourishment and oxygen to
the embryo
Canine Teeth Short
same length as other teeth
Foramen Magnum Forward
spinal cord opening, located forward, under skull
Extension Assignment
Each of the organisms in data table 1 belong to the kingdom Animalia and the phylum Chordata,
however they are a part of different classes. The class they belong to is based on the specific
characteristics that they have. Using your cladogram and Appendix A, can you determine which
characteristics go with which class? Make a T-chart with the class on one side and the
characteristic on the other.
Adapted from “Evolution & Nature of Science Institutes (ENSI/SENSI) Lesson Plan: Making
Cladograms”
i