The Arizona Hedgehog
Deborah A. Alongi
Purpose and General Overview
This unit of lessons is designed primarily to bring the scientific process skills of the research scientist into the high school classroom. The lessons mirror the efforts of the researcher (the author) in investigating this particular question, namely: Is the Arizona Hedgehog cactus truly an endangered, endemic subspecies limited to a very small range? The investigation applies molecular biology techniques to answer an evolutionary question. It demonstrates the often interdisciplinary nature of research science. The results of the investigation will be used to help make an environmental policy decision regarding protection of this subspecies.
This unit attempts to present all aspects of the research: field work to find specimens, review and analysis of relevant scientific literature, formulating a hypothesis based on the field work and literature, analyzing genetic variability within and among the populations in question and forming a conclusion based on the observed data. Finally, the students must demonstrate their understanding of the learning objectives by writing a formal scientific paper, gaining valuable practice in the skills of communicating knowledge in the process. As a part of their conclusion, each student should make a recommendation about whether or not the cactus should be protected.
Ideally this unit could serve as a model for teachers (or students) interested in conducting their own genetic studies using a plant from their own locality. The students would compare morphological differences versus genetic differences at a molecular level using RAPDs (Random Amplified Polymorphic DNA).
Bringing this research experience into the classroom presents a few logistical and practical problems. While field trips to collect specimens of an endangered species are not possible for high school students, an attempt to bring this experience into the classroom will be made in the form of a slide show. Additionally, isolating DNA from the tissue of Echinocereus species is difficult and involves the use of hazardous chemicals. Instead, a DNA isolation from the tissue of a desert plant which is far less difficult to work with will be performed by the students to give them first-hand experience in seeing a DNA extraction. Lastly, PCR amplification of DNA requires the use of a PCR Thermal Cycler, primers and Taq polymerase which are not usually readily available to high school teachers. Consequently, the amplification of the DNA with the appropriate primer(s) will be done in the research laboratory and digitized images of the resulting agarose gels (following electrophoresis) will be included in this unit. It may also be possible to obtain amplified Echinocereus DNA which can then be analyzed in the classroom by contacting me (Deborah Alongi) directly via e-mail at DAAlongi@aol.com.
Integration of Ecology and Evolution with Genetics
The highlight of this unit of lessons is the demonstration of the relationship between genetic variation in individuals and populations and their ecology and evolutionary pathways. The unit starts with a traditional morphological analysis of the plants and then moves to a genetic analysis to provide a different kind of information which may, or may not, support the hypothesis made based upon the traditional information. The students will not know the answer to this question until after analysis of the data and, incidentally, neither need the teacher know. This lesson is meant to be a truly open-ended investigation with the students relying upon their own observational and analytical skills to answer the question.
These lessons are intended for advanced biology students who have previously studied cellular and molecular biology concepts in some depth. A good background in taxonomy and evolutionary theory would also be beneficial. However, these lessons can be used in conjunction with other assignments and discussions to teach these concepts.
Background knowledge of the teacher need not be a major obstacle. Presenting the lesson can be a learning experience for the teacher as well, provided the teacher's understanding of the problem is at least as complete as the students' knowledge is expected to be by the student reading materials and student assignments prior to presenting the lesson. A workshop teaching the concepts and techniques used in these lessons may be taken by the prospective teacher.
Inquiries regarding technical questions, background information and availability of supplies/slides should be addressed to:
The University of Arizona
Department of Biochemistry and Molecular Biophysics
General Biology Program for Secondary Teachers