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Notes to Instructors
Chapter 26 Phylogeny and the Tree of Life
What is the focus of these activities?
One of the most valuable lessons we can teach students is that their minds should always
be open to new ideas and evidence. Scientific study is based on the accumulation of
What are the particular activities designed to do?
Activity 26.1 How are phylogenies constructed?
This activity is designed to help students get a better understanding of how taxonomy and
Activity 26.2 What is parsimony analysis?
In this activity, students apply parsimony analysis to three bird species using
Activity 26.3 Put yourself in the professor’s shoes: What questions would you ask?
This activity asks students to put themselves in the instructor’s shoes to see how exam
What misconceptions or difficulties can these activities reveal?
Activity 26.1
Activity 23.2 pointed out that many students are unfamiliar with, and therefore
uncomfortable with, making assumptions about the possible heritability of phenotypic
186 Notes to Instructors
words, what we know or teach as fact today may be modified in the future.
Activity 26.2
This activity reinforces the idea that our present understandings may be modified in the
Answers
Activity 26.1 How are phylogenies constructed?
Construct a modified concept map to relate the ideas of phylogeny and systematics listed
below to the phylogenetic tree on the next page.
• Begin by writing each term on a separate sticky note or piece of paper.
Terms
clade
cladistics
phylogenetic tree
homology
analogy
monophyletic
polyphyletic
paraphyletic
convergent evolution
shared primitive character
shared derived character
outgroup
ingroup
taxonomy
phylogeny
Activity 26.1 187
Chondrichthyes
(cartilaginous fishes: sharks and rays)
Actinopterygii
(ray-finned fishes)
Actinistia
(lobe-finned fishes)
Dipnoi
(lungfishes)
Amphibia
(frogs and salamanders)
Mammalia
(mammals)
(turtles)
tors)
Aves
(birds)
Myxini
(hagfishes)
Cephalaspidomorphi
(lampreys)
Osteichthyes
(bony fishes)
Milk
J
K
Feathers
Testudines
Lepidosauria
(lizards, snakes, and tuataras)
Crocodilia
(crocodiles and alliga
Use the understanding you gained from creating the concept map to answer the
questions.
1. Compare the taxonomy of a group with its phylogeny (in general terms).
2. On the phylogenetic tree shown earlier, are the groups that contain humans, whales,
crocodiles, and birds monophyletic, polyphyletic, or paraphyletic? Explain.
The group containing humans, whales, crocodiles, and birds would be considered
polyphyletic because no common ancestor is included.
Taxonomy Phylogeny
a. Definition or
purpose of a:
A taxonomy is a system for
naming and classifying
organisms.
A phylogeny categorizes
organisms based on their
evolutionary relatedness.
c. What similarities
could there be
between the
taxonomy of a given
group and its
phylogeny?
Phylogenetically related organisms often share similarities in
morphology. As a result, many taxonomies reflect
phylogenetic relationships as well.
Activity 26.1 189
3. Considering only the individual representative organisms in the phylogenetic tree
(e.g., bird, whale, frog), which can be used as good examples of analogy or
convergent evolution? As good examples of homology? Explain your reasoning.
The fish and whale are a good example of convergent evolution. Fish evolved in
aquatic habitats. The whale evolved from a mammalian terrestrial ancestor that took
4. In recent years, DNA sequence analysis has been used in developing phylogenetic
relationships among organisms.
a. What type of DNA has been used most commonly in this analysis? Why was this
type chosen over others?
The genes for the small subunit ribosomal RNA molecule tend to change
relatively slowly. As a result, they are used to determine relationships among
b. The phylogenies developed using DNA sequence analysis may differ from those
constructed using morphology and physiology. How do scientists know which
method is more correct?
5. Based on DNA sequence analysis three major domains of life have been proposed
What are the three major domains of life? What sets of characteristics place
organisms into one domain versus another?
190 Activity 26.1
Activity 26.2 What is parsimony analysis?
To determine relatedness among species, parsimony analysis is often used. In Figure
26.15 of Campbell Biology, 9th edition, parsimony analysis is applied to matched DNA
sequences from three species of birds. The same type of analysis can be applied to
1. Begin by recording in the table below the morphological characteristics of the three
bird species in Figure 26.15.
2. On the three possible phylogenies for these species (below the table) indicate the
number of changes that must have occurred for each of the proposed phylogenies to
be correct.
Activity 26.2 191
Major domains of life Key characteristics
For a more complete list, see Table 27.2.
Bacteria Bacteria display the prokaryote cell structure. Bacteria have
a circular chromosome. Bacterial cell walls contain
peptidoglycan. All bacterial species use the same type of
RNA polymerase. Bacteria use formyl methionine as their
initiator amino acid to start protein synthesis.
3. Based on your analysis, which of the phylogenies is most parsimonious?
How does this result compare to the result given in Figure 26.15?
Using the characteristics in the table, the second proposed phylogeny is most
4. Which of the proposed phylogenies (the one you developed or the one in
Figure 26.15) is more correct? Explain your answer.
Each is equally correct for the data used. Keep in mind that any analysis is only as
good as the data used. In both cases, only a few characteristics/bases were used. In
192 Activity 26.2
Traits A B C D E
Species Eye ring
(light/dark)
Red bar on
breast
(yes/no)
Red wing
bar (yes/no)
Light bar on
tail tip
(yes/no)
Beak shape
(curved/point)
Activity 26.3 Put yourself in the professor’s shoes: What
questions would you ask?
One of the best ways to study for an exam is to put yourself in the professor’s shoes. For
example, ask yourself: What questions would I ask about the material if I were Professor
__________. Asking and answering such questions are good practice for taking the actual
exam. They also help you to better understand and organize the major ideas and concepts
you have studied.
Write three exam questions designed to test how well a student understands the major
concepts in Chapters 22–26. Indicate the correct answer to each question and also tell the
reason why each alternative answer is incorrect. Your questions should be of the
following types:
I. Problem solving or application of a concept or principle to a problem
For example: The little-known hypothetical organism Skyscra parius is a long-necked animal
that feeds on the leaves of Australian trees that grow to heights of 30 feet. Being a hooved
animal, S. parius cannot climb trees, so it feeds much like modern-day giraffes do. Fossil
evidence indicates that the ancestors of S. parius had fairly short necks. Read the arguments
II. Translation: the ability to recognize concepts restated in a different form or to
restate concepts in a different form
For example: In what ways are the structure and function of the angiosperm seed and the
amniotic egg (in this example, the chicken’s egg) similar? In what ways are they different?
chicken eggs.
Activity 26.3 193
Write your exam questions in the spaces provided.
Exam Question 1:
Answer:
194 Activity 26.3
