Cladogram WS
Name
Period
Date
One way to discover how groups of organisms are related to each other (phylogeny) is to compare the anatomical
structures (body organs and parts) of many different organisms. Corresponding organs and other body parts that are
alike in basic structure and origin are said to be homologous structures (for example, the front legs of a horse, wings of a
bird, flippers of a whale, and the arms of a person are all homologous to each other). When different 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.
When we do studies in comparative anatomy, and find different numbers of shared and derived characters exist
between different groups, we can draw a diagram of branching lines which connect those groups, showing their different
degrees of relationship. These diagrams look like trees and are called "phylogenetic trees" or "cladograms" (CLAY-doegrams); see below for an example. The organisms are at the tips of the stems. The shared and derived features of the
homologous structures are shown on the cladogram by solid square boxes along the branches, and common ancestors
are as the intersections of two lines. The more derived structures two organisms share, the closer is their evolutionary
relationship -- that is, the more recently their common ancestor lived. 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.
Character tables are often made to help scientists make cladograms, an example is below. The character table lists
the shared and derived characteristics of the organisms that need to be put into the cladogram. Notice, on the taxa side
of the table, the organisms are listed from most primitive or ancient (lancelet) to least primitive or most recent (leopard).
They are listed in the same way at the top of the cladogram.
Answer the following questions IN YOUR OWN WORDS using your notes and the descriptions above.
1. What is an outgroup?
2. What is the purpose of the character table?
3. How are homologous structures related to cladograms?
4. How are both homologous structures and cladograms related to evolution?
5. On the cladogram above, which two organisms are most closely related? WHY?
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6. Fill in the cladogram below based on the character table. “0” means they do not have the
characteristic, “1” means they do have the characteristic. The characteristic that is the most
common among the taxa will be at the bottom of the cladogram in the box, while the one with
the least in common will be in the top box. The outgroup of the cladogram (nothing in common
with the other taxa), will be at the top left circle of the cladogram or the first “branch.” You can
double check your cladogram by looking at the characteristics in the chart. For example, ferns,
conifers, and flowering plants all have vascular tissue according to the chart, is it the same in your
cladogram? If not, you have made a mistake.
Taxa
Characteristics
flowers
wood and
seeds
vascular
tissue
Mosses
Ferns
Conifers
0
0
0
Flowering
Plants
1
0
0
1
1
0
1
1
1
7. It is quite simple to turn cladograms into dichotomous keys, fill in the blanks below using the
cladogram from #6:
1a) Has vascular tissue……………………..go to step
b) Does not have vascular tissue……..
2a) Has woods and seeds ………………..go to step
b) Does not have woods and seeds….
3a) Has
b) Does not have
………………Flowering plants
……
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8. Fill in the cladogram below based on the character table.
Taxa
0
Ray
finned
fish
0
0
sharks
Characteristics
feathers
egg with
shell
amniotic
egg
four limbs
bony
skeleton
Amphibians Rodents Crocodiles Birds
0
0
0
1
0
0
0
1
1
0
0
0
1
1
1
0
0
1
1
1
1
0
1
1
1
1
1
9. Now make the cladogram from #8 into a dichotomous key. Follow the same format as #7:
1a) Has bony skeleton……………………...go to step 2
b) Does not have bony skeleton ……...
2a)
b)
3a)
b)
4a)
b)
5a)
b)
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10. Now you need to make your own cladogram and dichotomous key based on the appearances of the
Norns below. You may use a character table if you wish, but you do not have to. Use the same names that
you figured out with the dichotomous key on the Dichotomous Key WS. You may use the characteristics
described on that WS to make your cladogram. Also, use the cladograms on the previous pages to guide
you. Note that since you are just going based on appearances, there are several correct ways to make a
table and cladogram for the species below. You may want to start by numbering the norns in the order
that they evolved and listing their characteristics below them (this will help you make a character table
and/or come up with the characteristics you will use in the cladogram). FYI- The loss of something can be
considered a characteristic (like loss of hair). You may need to use a separate piece of paper.
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