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The Arizona Hedgehog
Cactus:
Endangered Species or not?
Overview of Unit
A general overview of the unit is provided below. A more
detailed lesson plan can be obtained by clicking on the lesson title.
The detailed lesson plan includes specific objectives, teaching tips,
materials required, and links to all supplemental materials-- background
readings, handouts, slides, lab sheets and answer keys.
I. Presentation of the Problem:
A computer based slide show demonstrating the morphology
of the cactus populations in question (30-40 minutes). Teacher discussion
during the slide show of significant characters and differences among
the cacti. Students complete the activity sheet "Investigation of
the Problem" while watching and listening to the slide presentation.
Ten minute "wrap-up" to discuss the question being posed and to explain
the subsequent homework assignment.
Assignment: "Classification of Echinocereus triglochidiatus
and Geographical Ranges of its Varieties." Students read background
material and scientific literature to analyze the cactus populations
and then formulate a hypothesis.
Students present their lists of definitive characters
and hypotheses to the rest of the class. Teacher lists characters
on the board and then composes a working hypothesis with the consensus
of the class. (10-15 minutes)
Teacher introduces the concept of genetic analysis to
study similarities and differences among individuals within a population
and between populations. Discuss DNA isolation with students by asking
leading questions about cellular structure, biochemical molecules
found within the cell and their physical and chemical properties.
Assignment: Students read and complete the group assignment
"Chemical Detectives: How to find and isolate DNA" before performing
the actual DNA extraction.
II. Investigation of the Problem at the Molecular/Genetic Level
Lesson 3:
DNA Isolation from Plant Tissue
Students will follow the "DNA Isolation From Plant Tissue"
protocol to extract DNA from a suitable plant (pea plant tissue works
well).
Assignment: After performing the DNA isolation and reading
the background materials, the students will complete the assignment
"Isolation and Purification of DNA from Plant Tissue" to reinforce
and evaluate their understanding of the procedure.
Lesson 4: Polymerase
Chain Reaction and DNA Profiling
Teacher lecture and discussion of concepts in Polymerase
Chain Reaction and "DNA Fingerprinting" using one primer to amplify
nonspecific sites along the genome. Overhead transparency diagrams
of steps in PCR and in amplification of "random" regions of genome
with a short, nonspecific primer.
Assignment: Students read background materials "Polymerase
Chain Reaction (PCR) and DNA Profiling" and then complete the activity
sheet "Polymerase Chain Reaction: Amplification of DNA" for practice
and assessment of understanding.
Lesson 5: Electrophoresis
Analogy
Teacher review of previous lesson on PCR and how different-sized
fragments of DNA are generated by amplification with one "random"
primer. (10 min) Students participate in "An Electrophoresis Analogy"
to dramatize the principle behind DNA fragment separation by gel electrophoresis.
(30 minutes) Show overhead transparency "A DNA Agarose Gel" and discuss
how electric current moves the DNA molecules through the gel and the
relationship of the length of the fragments to the distance traveled
on the gel. (10 minutes)
Lesson 6: Electrophoresis
Protocols
Hand out "Electrophoresis Protocols" to each student.
Teacher discussion and demonstration of how to pour an agarose gel.
Assignment: Students will complete the worksheet "Gel
Electrophoresis and Analysis". Have the students read the "Electrophoresis
Protocols" in preparation for pouring their gels.
Lesson 7: Pour
and Load Agarose Gels
Students will work in groups of 3-4 to prepare and pour
their agarose gels, following the instructions contained in the hand-out
"Electrophoresis Protocols". Amplified DNA from a different individual
plant will be given to each student, to be loaded into the gels and
electrophoresed overnight.
Lesson 8: Analysis
of Data
Teacher discussion of what to look for to "score" bands
and make pair-wise comparisons. (10 minutes) Students then work in
groups to analyze the banding patterns of plants within populations
and between populations. (40-50 minutes). Polaroid pictures should
be taken of each gel with each lane being properly identified by each
group. Photocopies of all gel pictures (or digitized pictures) distributed
to each student group for data analysis.
III. "Publication" of Scientific
Papers or Scientific Posters
Lesson 9: "Publication"
of Scientific Papers and Posters
Teacher discussion about how to organize and prepare
a scientific paper or poster to report the procedure, results and
conclusions. (20-30 minutes)
Assignment: Students are to read the hand-out "Publication
of Procedure and Results" and refer to the hand-out "Evaluating the
Relationship of Autumn Buttercup to Some Close Congeners Using Random
Amplified Polymorphic DNA" for an example of a real, published paper
of a very similar study of another rare plant. Students either author
a scientific paper or make a scientific poster to present their procedure,
findings and conclusions. This may be an individual or group assignment.
In their conclusions, students should state whether the cactus populations
in Cochise county are the same as variety arizonicus, or not. An additional,
last assignment could be to have each student write a "letter" to
the U.S. Fish and Wildlife Service making recommendations about efforts
to protect this variety of hedgehog cactus.
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