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The Arizona Hedgehog
Cactus:
Endangered Species or not?
Lesson 4: Polymerase
Chain Reaction and DNA Profiling
Purpose:
The introduction of these two concepts will require considerable
explanation by the teacher with the aid of well-constructed diagrams.
PCR and DNA fingerprinting have become familiar in everyday life with
the use of these techniques for criminal investigations. A basic understanding
of them will help students to understand what they are hearing in the
popular media as well as showing that these techniques can be used equally
well to answer ecological and evolutionary questions.
Time:
One 50-60 minute class period
Materials Preparation:
- Overhead transparency diagrams of PCR and amplification with single-sequence
- 10-bp primers
- Student copies of background reading "Polymerase Chain Reaction
(PCR) and
- DNA Fingerprinting"
- Student copies of worksheet "Polymerase Chain Reaction Amplification
of DNA"
Student Objective(s):
- List and describe the three steps used in Polymerase Chain Reaction
and explain how repeating these three steps amplifies DNA exponentially.
- Explain how amplification of both genic and nongenic
DNA can provide a "DNA Fingerprint" for comparing similarities and
differences among individuals and populations.
Lesson Plan:
- Teacher discussion of the size and complexity of
higher organism genomes and the need to only look at small pieces
of the genome to compare differences.
- Review of the natural process of DNA replication
within the cell. List the basic steps on the board. This list can
be student generated. Pose the question, "How could the natural
process of DNA replication be modified to copy a DNA molecule in
a laboratory?" Students can brainstorm a procedure, before the explanation,
if you desire.
- Relate history of the development of PCR with
the discovery of the heat-resistant Taq polymerase. Use overhead
transparency to explain each of the three steps in one cycle of
PCR.
- Describe how "regular" PCR is used to amplify only
a specific, known region of the genome using two "flanking" primers.
Compare this process to using one primer of "random" sequence to
amplify many regions of the genome without knowing exactly where
the DNA has amplified from.
- Assign the background reading "Polymerase Chain
Reaction and DNA Fingerprinting" and the worksheet "Polymerase Chain
Reaction: Amplification of DNA."
Supporting Materials:
Other Resources:
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