Examples of Evolution
Teacher’s Guide
By Susan B. Parsons (NSF GK-12 Idaho State/Marsh Valley High)
Lesson Overview:
Subject Area:
1. Review examples of evolution and evolutionary principles
Biology
2. Introduce phylogenetic trees.
3. Create a phylogenetic trees based off sequence homology found in
GenBank.
Topic: evolution,
speciation, phylogenetic
trees
National Science Education Standards Addressed:
Audience:
11th Grade
Suggested time: 1 hour
Resources:
Materials:
Textbook
Computer lab
PowerPoint presentation Examples of Evolution
Worksheet
Learning Objectives:
1. Review examples of evolution, micro and macro scale.
2. Discuss speciation.
3. Introduce phylogenetic trees and their utility.
Background:
It takes time to properly teach evolution. This exercise is not intended as an introductory lesson
on evolution, but rather as a reinforcer for the general concepts of descent with modification,
divergence, and speciation. I added a slide regarding phylogenetic trees, as they attempt to describe
these relationships among taxa. The lecture portion of this lesson is not to be emphasized, but used as a
refresher. The real meat of this exercise is exploring GenBank, an on-line repository for DNA sequences
for a variety of plant and animal taxa. Students get the opportunity to observe real genomes, and look
at the relationships among a group of animals at a particular gene sequence, specifically that for
cytochrome B. Cytochrome B is particulary interesting because it is found in the mitochondria and plays
a role in energy production. This gene is present in humans, dogs, fish, and bacteria, and is generally
conserved across all animal taxa, making it a good candidate for looking at sequence homologies to
make phylogenetic inferences.
Assessment Strategy:
1. Students will be required to finish the attached worksheet, are expected to participate in class,
and will likely be tested on this material.
Teaching Tips:
1. Start off by briefly reviewing material presented in PowerPoint lecture.
2. Have students navigate to GenBank @ NCBI Genbank: http://www.ncbi.nlm.nih.gov/Genbank/ and
using the BLAST option:
BLAST: http://www.ncbi.nlm.nih.gov/blast/Blast.cgi
→Align two sequences using BLAST (bl2seq)
3. If you are not familiar with GenBank, it is highly advised that you spend some time navigating
through this site/database. Additionally, it is very helpful to have a computer lab that allows students to
watch how you navigate through GenBank using a smart classroom projector connected to your
computer. I started off by showing students a complete genome of some animal of their choosing,
versus the sections coding for specific genes (this case, CytB), and how that information is
labeled/stored/retrieved in the database.
4. Work through the worksheet as a class, and have a couple students put their versions of the
phylogenetic trees for a mosquito, bat, pigeon, and flying squirrel on the board (hopefully they’re
different, it makes things more interesting) based off morphological characteristics alone.
5. Have the students make comparisons of sequence similarity using the accession numbers below the
picture of each animal, and by looking at the “% identity” numbers produced by the BLAST program.
6. Hold a classroom discussion on how their trees changed when incorporating sequence homology
data and why. Additionally, ask students if using a single gene would be sufficient to create a
phylogenetic tree, and prompt them to devise ways of improving the analysis they just performed.
References:
Campbell, N.A., Reece, J.B., and L.G. Mitchell. 1999. Biology, 5th edition. Addison Wesley Longman, Inc.
Menlo Park, CA.
NCBI Genbank:
BLAST:
http://www.ncbi.nlm.nih.gov/Genbank/
http://www.ncbi.nlm.nih.gov/blast/Blast.cgi
→Align two sequences using BLAST (bl2seq)
Cladistics is the hierarchical classification of species based on evolutionary ancestry. The starting point
of cladistic analysis is a group of species and molecular, morphological, or other data characterizing
those species. The end result is a tree-like relationship-diagram called a cladogram.
Cytochrome B: In the mitochondrion of eukaryotes and in aerobic prokaryotes, cytochrome b is a
component of respiratory chain complex III. This complex is involved in electron transport and the
generation of ATP, and thus play a vital role in the cell.
Bat, Myotis spp. EF570884
Pidgeon, Columba spp. AF483335
Flying squirrel, Glaucomys. Spp.
Mosquito, Anopheles spp. AF062511
AY703880
Ia. Based off morphological characteristics, draw a cladogram representing the phylogenetic
relationships between these organisms.
Ib. How would adding functional or ecological characteristics affect your cladogram?
IIa. Using the BLAST database in Genbank, make pairwise comparisons of cytochrome b nucleotide
identities for these four organisms.
% Identity (similarity in sequence)
Bat-Pigeon
____________________________
Bat-Flying squirrel
____________________________
Bat-Mosquito
____________________________
Pigeon-Flying squirrel
____________________________
Pigeon-Mosquito
____________________________
Flying squirrel-Mosquito
____________________________
IIb. How does incorporating molecular/genomic data influence the arrangement of your cladogram?
Why would cytochrome b be a particular useful gene to make this sort of taxonomic comparison? What
type of genes would be useful for determining the relationship among closely related species (taxa)?