Name:______Date:______

Constructing an Evolutionary Tree from Biomolecular Data

By:

Focus statement: Students will compare the amino acid sequence of cytochrome C for several species. Based on this information they will construct a phylogenetictree. 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
  • 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.
  • SC.912.L.15.15:Describe how mutation and genetic recombination increase genetic variation.
  • 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
  • HS-LS4-1. Communicate scientific information thatcommon ancestry and biological evolutionare 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.’

Time frame: Roughlyan hour.

Resources:

  • Alternative versions of this handout:
  • DNA, amino acid, and protein explanation:
  • Molecular clock info

Materials:

  • “Constructing a Evolutionary Tree from Biomolecular Data” Worksheet
  • Amino acid sequences handout
  • PDF version here:

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.

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)

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 / Donkey / Whale / Chicken / Penguin / Snake / Moth / Yeast / Wheat
Horse / 0
Donkey / 0
Whale / 0
Chicken / 0
Penguin / 0
Snake / 0
Moth / 0
Yeast / 0
Wheat / 0

3)Using the top row of data, construct an evolutionary tree on the next page. Using the below steps.

  1. Draw a long diagonal line from the middle of the page to the bottom left corner.
  2. At the top right of this line write ‘horse.’
  3. Draw the branch of your most closely related species based on the lowest integer within the ‘horse’ row.
  4. Repeat this process with the second lowest integer.
  5. 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?