Name:__________________________________________________________Date:_________________
Constructing an Evolutionary Tree from
Biomolecular Data
By:
Name:__________________________________________________________Date:_________________
Focus statement: Students will compare the amino acid sequence of cytochrome C for several
species. Based on this information they will construct a phylogenetic tree. A discussion will
then ensue how the phylogenetic tree could be tested and further refined using other data
(anatomical, other genes, fossil evidence, biogeographic, etc.).
Within this lesson students will compare data sets of amino acid sequences. From these
sequences they will use the number of differences to approximate how closely related different
species are. From there they will interpret the significance of the observations. Particular focus
will be placed on having students think through different ways of finding supporting or
disconfirming data.
Thinking Skills: Students will have to ascertain data, organize it into data tables, and then use
that information to construct a phylogenetic tree.
Learning Objectives:
 Student will be able to use data to construct an evolutionary tree.
 Students will be able to explain how homology supports the theory of evolution.
Standards
 FL
o SC.912.L.15.1: Explain how the scientific theory of evolution is supported by
the fossil record, comparative anatomy, comparative embryology,
biogeography, molecular biology, and observed evolutionary change.
o SC.912.L.15.15: Describe how mutation and genetic recombination increase
genetic variation.
o SC.912.L.15.2: Discuss the use of molecular clocks to estimate how long ago
various groups of organisms diverged evolutionarily from one another.
 NGSS
o HS-LS4-1. Communicate scientific information that common ancestry and
biological evolution are supported by multiple lines of empirical
evidence. [Clarification Statement: Emphasis is on a conceptual understanding
of the role each line of evidence has relating to common ancestry and biological
evolution. Examples of evidence could include similarities in DNA sequences,
anatomical structures, and order of appearance of structures in embryological
development.]
Prerequisite Knowledge
 Student will be able to interpret an evolutionary tree.
 Student will be able to define what an amino acid sequence is.
 Student will be able to define what a molecular clock is.
Preassessment questions to gauge student’s prior knowledge:
 When students are provided a simple evolutionary tree example they are able to interpret
that node proximity determines relatedness (as opposed to the common misconception
that branch proximity determines relatedness). Students can define ‘homology’ and
‘amino acid sequence.’
Name:__________________________________________________________Date:_________________
Time frame: Roughly an hour.
Resources:
 Alternative versions of this handout:
o http://www.indiana.edu/~ensiweb/lessons/mol.bio.html
 DNA, amino acid, and protein explanation:
o http://www.nature.com/scitable/topicpage/nucleic-acids-to-amino-acids-dna-specifies935

Molecular clock info
o http://evolution.berkeley.edu/evosite/evo101/IIE1cMolecularclocks.shtml
Materials:
 “Constructing a Evolutionary Tree from Biomolecular Data” Worksheet
 Amino acid sequences handout
o PDF version here: http://www.indiana.edu/~ensiweb/lessons/molb.dat.pdf
Attention Grabber and Intro: Let students know that they will be solving a mystery today and
determining using biomolecular evidence which species are most closely related. Doing so will
allow us to reconstruct a hypothesis about evolutionary history and determine which species
most likely recently split off from other species.
At the beginning make sure that students understand what an amino acid sequence. It is the
beginnings of a protein and is translated from RNA which is transcribed from DNA. Explain
that in this case we will be looking at cytochrome C, which is a highly conserved sequence and is
involved in respiration and metabolism (the obtaining of energy from sugar and oxygen).
Because it is so important to the survival of different species it is highly conserved. Mutations
that are beneficial or not harmful are highly rare and only happen very infrequently. Because
that is the case we can use these highly unusual and rare mutations to determine not only how
closely related species are, but also to estimate how long ago two species diverged from each
other.
Students will then be introduced to the concept of phylogenetic trees. Several examples will be
drawn on the board and typical misconceptions and mistakes will be addressed. Willing students
will then perform example on the white board after I tell them who which mock species are most
closely related.
Activity: Students will be handed data sheet and worksheet and allowed to work in groups of
four. Students are allowed to divide up the task of counting amino acid differences between
species. However, each student should make their own evolutionary tree. Demonstrate to the
students how to properly count the differences in amino acid sequences. Make sure they
understand that the sequences break on to another line and where to write their answers.
Closure: Help students understand that the work that they just completed is very similar to the
work done by many thousands of scientists across the globe to help construct an ever growing
tree of life. The final discussion will involve how we can disprove or support the evolutionary
hypotheses we have just produced.
Name:__________________________________________________________Date:_________________
Accomodations: Some students may be unable to draw the phylogenetic tree. Since they will be
working in groups others are allowed and encouraged to help but also admonished to only draw
what they are told to by the student unable to draw. The same goes for students that are unable
to determine how many differences there are between amino acid sequences due to difficulty
tracking with their eyes or visual impairment. Student learning goals and vocabulary will be
prominently placed at the front of the room so that students will be able to see visually the
vocabulary involved with the lesson and so that they can consult the information throughout the
lesson.
Assessment (see worksheet)
Name:__________________________________________________________Date:_________________
Constructing a Evolutionary Tree from Biomolecular Data Worksheet
Today you will construct an evolutionary tree based on biomolecular data. Doing so will allow you to
create a hypothesis about the evolutionary history of several species.
Background: Some DNA is converted into mRNA which can then be turned into a chain of amino acids
called a protein. After one species splits into two species parts of their genome act like molecular
clocks, which changed at fixed, regular amounts. One such molecular clock is the sequence for
cytochrome C. We will analyze the differences in cytochrome C amino acid sequences between 9
species.
1) Using the “Amino Acid Sequences Data” handout, fill in the blanks with the number of amino
acid differences between the paired sequences. This is the only part of the worksheet that you
can divide the task among members in your group and share data.
2) Using the data from the step above fill in this chart.
Horse
Horse
Donkey
Whale
Chicken
Penguin
Snake
Moth
Yeast
Wheat
Donkey
Whale
Chicken
Penguin
Snake
Moth
Yeast
Wheat
0
0
0
0
0
0
0
0
0
3) Using the top row of data, construct an evolutionary tree on the next page. Using the below
steps.
a. Draw a long diagonal line from the middle of the page to the bottom left corner.
b. At the top right of this line write ‘horse.’
Name:__________________________________________________________Date:_________________
c. Draw the branch of your most closely related species based on the lowest integer within
the ‘horse’ row.
d. Repeat this process with the second lowest integer.
e. Repeat until the entire tree is filled in.
4) Explain why species separated by much time often have sequences that are very different.
5) If on average 1 change happens every 15 million years, calculate when each species diverged
from the horse and add this information to your evolutionary tree.
6) What other information could be used to support or contradict the evolutionary tree you have
just created?