Download Chapter 24

CHAPTER 24: GENOME EVOLUTION
WHERE DOES IT ALL FIT IN?
Chapter 24 combines the information on genomic organization with the phylogeny presented in
Chapter 23. The concept of population genetics must be reviewed to help students understand the
applications of the principles covered in Chapter 24. Chapter 24 is essential to explain the
adaptation of organisms covered later in the textbook
SYNOPSIS
A new and exciting area of biology called comparative genomics is generating new interests and
building links between genetics, evolution, and development. Comparative genomics is
addressing areas such as: How have complex traits evolved? What are the origins of genomic
differences? How have developmental mechanisms evolved?
Evolutionary histories of species are inscribed in the nucleotides of the DNA molecules in their
genomes. Scientists are finding many similarities in DNA sequences in species that had a
common ancestor hundreds of millions of years ago. These discoveries are especially interesting
because evidence suggests that common or similar genetic sequences have different expressions
in different species. Examinations of conserved DNA sequences of vertebrates such as the
pufferfish and a mouse are leading medical scientists toward a better understanding of the basis
for human genetic disorders and diseases.
Investigators looking at genome reorganizations have begun reexamining chromosome 2 in
humans in search of more answers for just how closely related the great apes (orangutans,
gorillas, chimpanzees, and humans) are. In another study of the malarial causing protist,
Plasmodium, researchers are exploring proteins, which promote fatty acid production. This
knowledge could be used to design a treatment that would eliminate the parasite by shutting
down the production of critical fatty acids necessary for its life. This fatty acid production is
directed by certain proteins, which are encoded for by genes with the genome of Plasmodium.
Genomic differences, which can lead to evolution of new species, can be initiated in six different
ways, from single gene mutation to integration of DNA form one species into a different species.
In a way of thinking about this, consider merging all or part of one species genome with another,
if it works then a new species might evolve and be acted on by natural selection.
Horizontal gene transfer has caused a rethinking by some biologists in regards to the “tree of
life” and its three domains. Some argue that it is more like a net or web of life rather than a tree
with entirely separated branches. They offer that various genes could have been laterally
transferred across branches rather that up the branch in a vertical fashion.
LEARNING OUTCOMES
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Know what the term genome means and what it means to science to have elucidated a
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complete genome of a species.
Understand why researchers have honed in on conserved DNA sequences between other
vertebrates and humans.
Describe why even though mice and humans share 99% of their genes, there are so many
differences between the species.
Know how chromosomal rearrangement can lead to the evolution of new species.
Understand the mechanism of how an herbicide, which is used to kill weeds, might be used
to kill the protist, Plasmodium.
Be able to explain the new field of biology known as comparative genomics.
List and give an example of the six different ways in which a genome can change over time.
Distinguish between ortholog, paralog, and a pseudogene.
Compare horizontal gene transfer with lateral gene transfer.
Be able to provide a plausible explanation of why humans have more transposons than
Drosophila, even though Drosophila have been around for hundreds of millions of years
longer than humans.
Understand how convergent evolution works when different genes are recruited in different
species. Give an example.
COMMON STUDENT MISCONCEPTIONS
There is ample evidence in the educational literature that student misconceptions of information
will inhibit the learning of concepts related to the misinformation. The following concepts
covered in Chapter 24 are commonly the subject of student misconceptions. This information on
“bioliteracy” was collected from faculty and the science education literature.
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Students believe that all genes program for visible traits
Students believe that only the observable phenotype is subject to selection
Students believe that DNA variation between different organisms if always very high
Students are unfamiliar with the degree of conserved genes between unrelated organisms
Students believe that acquired traits are inherited
Student believe evolution is driven to make “better” organisms
Students believe that organisms adapt to change rather than being selected
Students do not take into account mutation in determining population genetics
Students believe “fitness” is an absolute set of characteristics
Students believe that species are genetically distinct and fixed
INSTRUCTIONAL STRATEGY PRESENTATION ASSISTANCE
There is an interesting and current paper in the November/December 2003 issue of the American
Scientist entitled “Survival of the Fittest Molecule.” It addresses issues raised in this chapter at
can be found at
http://www.americanscientist.org/template/AssetDetail/assetid/28360;jsessionid=aaa5LVF0.
Purchase specimens of pure yellow corn lacking visible transposon activity and decorative corn
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showing transposon effects.
HIGHER LEVEL ASSESSMENT
Higher level assessment measures a student’s ability to use terms and concepts learned from the
lecture and the textbook. A complete understanding of biology content provides students with the
tools to synthesize new hypotheses and knowledge using the facts they have learned. The
following table provides examples of assessing a student’s ability to apply, analyze, synthesize,
and evaluate information from Chapter 24.
Application
Analysis
Synthesis
Evaluation
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Have students explain the factors leading to the evolution of human
influenza which was originally a pig disease.
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Have students describe how endosymbionts contribute to an organism’s
evolution.
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Ask students to explain the implications of mutations to transposons.
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Have students explain the role of agriculture in the evolution of new
human diseases.
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Ask students to assess the value of a mutation that increases the mutation
rate of nearby genes.
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Ask students to impact of chemicals that damage DNA on the genomic
evolution of an organism.
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Ask students to assess the evolutionary consequences of genetic changes
that reduce non-coding DNA in an organism’s genome.
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Have students design an experiment to show if gene expression differs
between two similar genomes isolated from samples of frozen ancient
animals.
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Ask students explain how comparative genomics can be used to develop
better drugs to treat infectious diseases.
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Ask students to compare the relative importance of genomic versus
endosymbiont changes in determining the evolutionary divergence of a
species.
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Ask students explain the benefits and risks of producing new crops by
forming polyploid plants.
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Ask student to determine the validity of a drug that is guaranteed not to
produce resistance in the disease organism it is treating.
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VISUAL RESOURCES
Obtain butterflies from the insect museum to let students observe the different eyespot patterns in
different species of butterflies.
Demonstrate horizonal transfer and lateral transfer by handing something to the person directly
in front of you and then demonstrate lateral transfer by passing something to the person beside
you.
IN-CLASS CONCEPTUAL DEMONSTRATIONS
A. Name that Change Game
Introduction
Arthropods are excellent models for predicting the phenotypic changes that led to their
great diversity. This demonstration provides students with the opportunity to hypothesize about
the types genomic changes that could have led to the phylogenetic diversity of arthropods.
Materials
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Computer with live access to Internet
LCD projector attached to computer
Web browser bookmarked to Arthropod Story
http://evolution.berkeley.edu/evolibrary/article/3_0_0/arthropodstory
Procedure & Inquiry
1. Review the principles of classification with the class.
2. Go through Part 1 (Introducing the Arthropods) and Part 2 (What is an Arthropod) of the
on-line lesson.
3. Ask the class to list major features of the arthropods that make them unique from their
worm ancestors. Then have the class consider the types of genetic changes needed to
achieve those unique differences.
4. Now go to the Cambrian Critters section and ask the students to look at the differences
and similarities of the ancestral arthropods compared to the modern ones.
5. Finish up by going through the remaining on-line lessons.
6. Have the students quickly summarize what they learned.
USEFUL INTERNET RESOURCES
1. Mitochondrial DNA is often overlooked at a tool for understanding genetic changes
within an evolving population. The University of California at Berkeley provides an on-
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line lesson for investigating the genomic changes in mitochondria. This website is an
excellent supplement to a lecture on the material in Chapter 24. It is available at
http://www.geneticorigins.org/geneticorigins/mito/mitoframeset.htm.
2. A good website for teaching the principles of transposons is available form Palomar
College. It provides a simple to understand tangible model demonstrating transposons.
The website can be found at http://waynesword.palomar.edu/transpos.htm.
3. Students may be surprised to learn that cancer cells undergo evolutionary genomic
changes that enhance their survival. At website provided by the Howard Hughes Medical
Institute is useful for gathering classroom information about cancer evolution that can be
related to the information in Chapter 24. The website is available at
http://www.hhmi.org/biointeractive/cancer/cancer_evolution.html.
4. Cases studies are an effective tool for getting students interested in genomic evolution.
The University of Buffalo provides a teaching case study called “Si el Norte Fuera el Sur:
A Case of Squirrel Monkey Identities”. It has the students apply the principles of
population genetics and genomic evolution to decisions of categorizing a new species.
The case study can be found at
http://www.sciencecases.org/dinosaur_evolution/dinosaur_evolution_notes.pdf
LABORATORY IDEAS
Phylogenetic changes due to genomic mutations can be investigating using comparative
anatomy approaches. This lab session has students comparing the bones of rodents from owl
pellets to human bones on an articulated skeleton. Students will be asked to hypothesize the
types of genomic changes involved in the differences seen in the comparable bones.
a. Students should be provided with the following materials to perform this open-ended
inquiry.
a. Owl pellets
b. Dissecting probes
c. Paper
d. Cellophane tape or glue
b. Introduce students to the owl pellet by doing a virtual pellet dissection using the Virtual
Owl Pellet website at http://www.kidwings.com/owlpellets/virtual/vopfinal.htm.
c. Hand out the Owl Pellet Bone Chart found at
http://www.kidwings.com/teacher/owlpellets/bonechart.htm.
d. Then tell the students that you want them to collect a representative rodent from the owl
pellet. They should tape or glue the bones to a sheet of paper
e. Have the students compare the rodent bones to the comparable human bones
f. The students should be asked to hypothesis the types of genomic changes that would
explain differences between the homologous rodent and human bones.
LEARNING THROUGH SERVICE
Service learning is a strategy of teaching, learning and reflective assessment that merges the
academic curriculum with meaningful community service. As a teaching methodology, it falls
under the category of experiential education. It is a way students can carry out volunteer projects
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in the community for public agencies, nonprofit agencies, civic groups, charitable organizations,
and governmental organizations. It encourages critical thinking and reinforces many of the
concepts learned in a course.
1. Have students prepare a PowerPoint presentation on genomic evolution for high school
teachers.
2. Have students tutor high school students covering evolution in a biology class.
3. Have students work with an environmental group working to preserve biodiversity of the
region.
4. Have students do an owl pellet and human bone comparison activity at a local elementary
school.
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