Bio 7: How to Make a Cladogram
Bears and their relatives: an exercise in clade construction
Part I
Biologists use a variety of traits to reconstruct the evolutionary affinities among species and larger groups of
organisms. This exercise will introduce you to the logic of the clade by constructing a cladogram for a group of
mammals based on a relatively small set of traits. A “trait” is any measurable aspect of the organism; for extant
organisms, traits can be morphological, behavior, physiological, genetic and/or molecular.
Bears are one of many groups for which there is some disagreement among scientists regarding their exact
relationships. Imagine you have a long-term fascination with bears and have decided to form your own hypothesis
regarding the relationship of the great panda to other bears and their closest relatives. You come up with a list of
traits for which you can find data on reliable internet sites, and construct the table illustrated below. Using the data in
this Table, draw a branching diagram on the following page that represents your reconstruction of the evolutionary
divergences that occurred in this lineage. Use a pencil so you can erase, or make a draft on a piece of scratch paper.
An X means that the corresponding taxon possesses the trait in question; an empty box means the species lacks that
trait; in other cases, the trait is described. Indicate on your branching diagram the point at which you think each trait
evolved.
X
Asiatic Black Bear
X
X
Sun Bear
X
Polar Bear
Claw curvature
Climb trees
No
Medium
X
Short
72
No
Strong
X
X
Short
72
No
Strong
X
X
X
Short
72
No
Medium
Brown Bear
X
X
Short
72
No
Medium
Giant Panda
X
X
Short
42
No
Medium
X
Red Panda
X
X
Long
36
partly
Medium
X
X
Claws retract?
38
Translucent fur
Long
Shoulder hump
X
Smooth, short coat
Rings on tail
X
Diploid number (2N)
Tail length
Raccoon
Common Name
Carnassial cheek
teeth
Females produce
milk for young
*Hint: Work from left to right through the table below when ordering the branches in your diagram.*
X
X
X
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What principles did you use to construct your cladogram?
Compare your cladogram with others in your discussion section. Can you resolve the differences?
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Part II.
DNA Sequences
Scientists also use molecular information to determine evolutionary relationships. One common
technique is to compare DNA sequences from the same gene between different organisms.
Below are DNA sequences from 5 animal species found in a scientist’s lab notebook. You can
help her construct a phylogenetic tree that illustrates how these species relate to each other based
on how many differences there are in the nucleotide sequence for each pair of species, also
known as the genetic distance. You will first need to fill in the data table with the number of
differences in the nucleotide sequences. Then using the information in your data table, draw out
the evolutionary relationship for these animals.
Common Name
Species Name
DNA Sequence
Giant Panda
Ailuropoda melanoleuca
Red Panda
Ailurus fulgens
Polar Bear
Ursus maritimus
Brown Bear
Ursus arctos
Raccoon
Procyon lotor
GTTAGTATAA
GTCGATGAGA
GCTCTCATAA
GATCTCATAA
GTCGATTCGA
Giant Panda
Red Panda
Polar Bear
Brown Bear
Raccoon
Giant Panda
Red Panda
Polar Bear
Brown Bear
Raccoon
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Part III.
False thumb
Tendency to
hibernate
Number of adult
teeth
Common Name
Finally, here are a few more traits of the 7 species on page 1. Map these traits onto your
cladogram on page 2.
Raccoon
40
None
Asiatic Black Bear
42
Variable
Sun Bear
42
None
Polar Bear
42
None
Brown Bear
42
Strong
Giant Panda
40
None
X
Red Panda
40
None
X
Does the use of these traits help you to build a better cladogram? Why or why not?
How can you explain the occurrence of traits that do not fit neatly into the phylogenetic
relationships you found on pages 2 and 3 of this handout?
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