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LESSON
PLAN: TRACING
GENETIC ANCESTRY USING DNA MICROARRAYS
Background,
Activities and Critical Analysis
By
Susan Senn, a retired biology teacher Subject(s):
biology or biotechnology Estimated
Time: One 90- or two 45-minute periods with options to extend. Grade
Level: 9-12 (lesson can be modified for lower grades) Overview:
Students will: 1.
Read and discuss an article about genetic ancestry and genetic ancestry testing.
2. Apply knowledge
of DNA and heredity to understand DNA microarrays, and concepts of genetic mutation
and ancestry tracking.
3.
Mimic the function of a DNA microarray used for genetic ancestry analysis by completing
a paper-and-pencil activity.
4.
Discuss the ethics of genetic testing in medical research.
TO
MAKE THESE LESSONS BETTER  Correlation
to National Standards Materials Background
If you ask people
where their ancestors came from, most will answer with a country - like Ireland,
Germany, or El Salvador. But most people do not know about their 'ancient' ancestry:
Are they mostly or partly Asian, African, European or Indigenous American? Though
humans share 99.9 percent of their DNA, mutations found in the 0.1 percent that
differs can be used to trace ancient genetic ancestry. As DNA is passed from parents
to offspring, mutations build up, creating a genetic family tree that encodes
a wealth of information. Scientists have correlated many of these mutations, DNA
markers in form of "single nucleotide polymorphisms" and "microsatellites," with
ancestral groups from around the world today, and in doing so they have reconstructed
human migration maps dating back to a genetic "Eve." Now, many companies offer
tests that use DNA microarrays, also called gene chips, to compare DNA markers
in samples with those found in hundreds of ancestral groups. The result is a personal
genetic profile that can be used to give information about the geographic component
of a person's past. (Note: Links at the end of this lesson plan have more
information about genetic ancestry and DNA microarrays.) Vocabulary
- DNA: The chemical
that carries the genetic instructions for making living organisms
-
Gene chip: Sets of miniaturized chemical reaction areas used to test DNA fragments
-
Genome: All the DNA contained in an organism, including the DNA within the cell's
nucleus and the mitochondria
-
Haplogroup: A collection of similar DNA markers that mark branches in genetic
evolution and can indicate common ancestry
-
Microsatellites: Genome regions with repeating sections of DNA sequences; used
as markers
-
Mitochondria: The parts of the cells that generate energy. Mitochondria have their
own DNA which is passed from mothers to offspring.
-
Nucleus: The central cell structure that holds DNA
- Restriction
Enzymes: Enzymes that recognize a specific sequence of double-stranded DNA and
cut the DNA at that site. Restriction enzymes are often referred to as molecular
scissors.
-
Single Nucleotide Polymorphisms: Genome variations that occur when a single DNA
nucleotide (A, T, C, or G) is altered
-
Y chromosome: One of the two chromosomes that specify gender. Humans have two
kinds of sex chromosomes: X and Y. Females have two X chromosomes and males have
one X and one Y.
PART
I: Discussion: Human Migration and the DNA Microarray
(45 minutes) Procedure
1. Review concepts of DNA, heredity and mutation. This lesson could follow a DNA
extraction lab. 2.
Engage the students with a question: How
could you use DNA to find out about human history? Encourage
the students with follow-up questions: - What
is it about DNA that makes each of us unique?
- What
sort of information about humans can you get from DNA?
- Where
do mutations come from?
- Can
heredity apply to mutations?
- What
is "junk DNA?"
- Can
"junk DNA" have heritable mutation?
3.
Distribute and/or share the Online NewsHour article entitled, "DNA Kits Provide
Picture of Past" available at http://www.pbs.org/newshour/indepth_coverage/science/dna/science.html
. (This article could be handed out at the end of the previous class.) As a class,
read the article and discuss the use of genetic markers in the field of genetic
genealogy. Review vocabulary when needed. 4.
Show the genetic
migration map (PDF). Point out that the letters on the map correspond to some
mitochondrial DNA (mtDNA) haplogroups. Then, using the map, ask the students to:
- Identify the time
and location of "mitochondrial Eve". Discuss how scientists could have
analyzed mitochondrial DNA to determine the existence of this maternal ancestor.
- Identify
the approximate times at which human first expanded into the following continents:
Asia, Australia, Europe, North America, South America.
- Determine
which continent was populated first? Which continent was populated most recently?
- Postulate
why the continents were populated in the pattern shown on the map.
- Think
about how migration patterns changed due to climate change, specifically after
the end of the last ice age (about 10,000 years ago).
5.
Revisit the opening question: How could you use DNA to find out about an
individual's history? - Introduce
the DNA microarray and show the example
DNA microarray procedure (PDF) as an overhead or handout, making note that
the students will be going through the same steps in the next lesson.
6.
Review new concepts. PART
II: Hands-on Activity: Tracing Human Ancestry with DNA Microarrays
(45
minutes) Procedure 1.
Tell students they will be using an on-paper version of a DNA microarray to determine
human ancestry. 2.
Review concepts of heritable mutation, and how mutations in DNA can be used to
trace ancestry, DNA microarrays and DNA base pairing. 3.
Split the class into teams of four students, and provide one set of materials
for each group: a copy of the instructions
and worksheet, microarray
grid master, microarray
analysis grids and the four
human cDNA fragments. Provide guidance for the exercise. You may assign 1
of the 4 DNA strands to the students or they can pick strands in groups. Leave
the DNA microarray procedure on an overhead projector as the students do the activity.
Students can color, using different colored pencils, each human cDNA sequences.
After the students have 'hybridized' the genes onto the Microarray Grid Master,
they will be able to analyze their results and determine the ancestry of each
of the four humans. 4.
Discuss the results and assign homework activities (optional). Collect the worksheets
at the end of the class.
Homework
Activities Download
the homework questions (PDF) and answer
key (PDF).
Write
a one-page essay on the ethical issues surrounding genetic ancestry tests. Be
ready to discuss your thoughts in the next class. Use your answers to one or more
of these questions to help you develop your essay. 1.
Can genetics be used to define race?
2.
How much faith can you put in a result from a DNA ancestry test?
3.
What are some ethical issues associated with profit-making companies collecting
genetic information?
4.
Can potential harm caused by genetic testing be balanced by potential good done
when applied the tests for medical research? Additional
Resources for Teachers The
following Web sites are excellent descriptive and demonstrative examples of DNA
microarray technology:
The
Online NewsHour's in-depth coverage of genetic ancestry, "Search for Ancestors,"
available at http://www.pbs.org/newshour/indepth_coverage/science/DNA/
and "DNA Kits Provide Insight into Genetic Ancestry", available
at
http://www.pbs.org/newshour/bb/science/july-dec06/ancestry_07-20.html General
information about microarrays:
http://www.hhmi.org/biointeractive/genomics/microarray.html
(Howard Hughes Medical Institute)
http://www.ncbi.nlm.nih.gov/About/primer/microarrays.html
(National Center for Biotechnology Education)
http://affymetrix.com/corporate/outreach/educator.affx
(Affymetrix)
http://www.bradenton.com/mld/bradenton/news/local/15256754.htm
(Herald Today / Associated Press) Microarray
movies:
http://www.bio.davidson.edu/courses/genomics/chip/chip.html
(Davidson)
http://learn.genetics.utah.edu/units/biotech/microarray/
(Genetic Science Learning Center, University of Utah) Extension
Activity Using
the above links, have students answer these questions:
1.
How are the various types of cells in our bodies different from one another, genetically
speaking?
2. What does 'gene expression' mean?
3. Why do researchers generally
purchase already manufactured microarrays from biotechnology companies rather
than make them in their own labs?
4. Each spot on the microarray corresponds
to what?
5. A DNA sequence of C-A-T-T-G will stick to, or hybridize to the
following base sequence ____________ to form double-stranded DNA.
6. DNA sequence
arrays can be used to detect what?
7. There are two great values of using
microarray technology. What are they?
8. What is the biological source of
restriction enzymes?
National Standards
Correlation
to National Science Standards
(from the National Science Education Standards
site at http://books.nap.edu/html/nses/html/6e.html):
Content
Standard C: Life Science
Content
Standard E: Science and Technology
Content Standard F: Science in Personal
and Social Perspectives
McRel
Compendium of K-12 Standards Addressed:
Science
Standard 4. Understands the principles of heredity and related concepts
Standard 7. Understands biological evolution and the diversity of life
Standard
12. Understands the nature of scientific inquiry
Standard 13. Understands
the scientific enterprise Technology
Standard 6. Understands the nature and uses of different forms of technology
Geography
Standard 9. Understands the nature, distribution and migration of human populations
on Earth's surface Language
Arts
Standard 1. Uses the general skills and strategies of the
writing process
Standard 3. Uses grammatical and mechanical conventions in
written compositions
Standard 4. Gathers and uses information for research
purposes
Standard 5. Uses the general skills and strategies of the reading
process
Standard 7. Uses reading skills and strategies to understand and
interpret a variety of informational texts
Standard 8. Uses listening and
speaking strategies for different purposes Working
with Others
Standard 1. Contributes to the overall effort of a
group
Standard 3. Works well with diverse individuals and in diverse situations
Standard 4. Displays effective interpersonal communication skills About
the Author Susan Senn retired four years ago from teaching Regular, Intensified
and AP Biology. For the past four years, she has served as a biotechnology resource
teacher. She recently wrote and co-taught a year-long course in Biotechnology
Techniques and Applications. To
find out more about opportunities to contribute to this site, contact Leah Clapman
at extra@newshour.org. | 
