Let's Build a Cladogram!
Introduction: C/adistics is one ofthe newest trends in the modern classification of organisms. This method
shows the relationship between different organisms based on the presence or absence of
...
Let's Build a Cladogram!
Introduction: C/adistics is one ofthe newest trends in the modern classification of organisms. This method
shows the relationship between different organisms based on the presence or absence of certain characteristics
called "derived characters". Derived cl,aracters are the unique characteristics of a particular group of
organisms. These characteristics are "evolutionary innovations" that arose in one group of organisms, but are
not found in the older members ofthe lineage. Based on these derived characters, cladistics is used to
determine the sequence in which different groups of organisms evolved. The organisms and their derived
characters are then illustrated on a diagram called a cladogram. A c/adogram shows the evolutionary
relationships among groups of organisms. Organisms that are grouped more closely on a cladogram share a
more recent common ancestor than those farther apart.
Purpose: 1) To make careful observations to determine the derived characters of a group of organisms.
2) To arrange the derived characters into a cladogram showing the relationships between the
organisms.
Materials: Pictures oflamprey, trout, caecilian, turtle, cat, gorilla, and human
Procedure:
1. Make careful observations of the animals in the pictures you have been given. As you study each picture,
determine ifthe animal has any of the characteristics that you see in the data table below.
2. Ifthe characteristic is present in the animal, place a"+" in the correct column, indicating that the animal
has that particular characteristic.
3. Ifthe characteristic is absent in the animal, place a" - "in the correct column, indicating that the animal
does not have that particular characteristic.
Table of Derived Characters:
Characteristic
Organism Jaws Limbs Hair Lungs Opposable Upright, erect
thumb posture
Lamprey
Trout
Caecilian
Turtle
Cat
Gorilla
Human
Total
4. Fill in the line ofthe data table marked "total". Count how many organisms possess each characteristic.
For example: How many organisms have jaws? List this number for the total. Determine the total for
each characteristic.
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