You and your students are about to embark on the study of genetics. Can you remember your first exposure to genetics? It was probably like mine, in 10th grade, and consisted of going through the crosses and back crosses that the Austrian monk, Gregor Mendel, carried out with garden peas. You may remember using Punnett squares to figure out the famous ratios of Mendelian genetics. You and I can appreciate these experiments as being some of the most beautiful in the history of biology. However, that does not mean that today's middle grade students will be fascinated by the genetics of pea plants. We introduce students to genetics by having them observe and measure human traits. They study themselves to learn about constancy and variation. Then we introduce them to examples of dog breeding to figure out the rules governing the inheritance of a trait.
The next step is still not Mendel's peas, but aspects of genetics that were unknown to Mendel. Cellular and molecular details of genetics are in the news every day and are the subjects of popular movies and TV programs. Chromosomes, DNA, genes, cloning, and mutations are common concepts, but not necessarily well understood. Therefore, we explore the cellular and molecular biology underlying inheritance-mitosis, meiosis, fertilization, chromosome replication, and the genetic code. With that background, students can see the pea plant experiments as great examples of how genetics works, rather than as the focal point of their study of genetics.
The relevance of genetics becomes obvious with consideration of human genetic disorders and the issue of genetic counseling. The unit concludes with a discussion of genetic engineering and the Human Genome Project-subjects that are in the news practically every day, subjects that will continue to touch your students whether or not they continue to study science. Your students will end this unit with knowledge of genetics that will enable them to form their own opinions on such issues as genetically engineered crops, environmental mutagens, genetic testing, and the use of DNA as forensic evidence.
As with all the HumBio curricular units, this unit is intended to promote interdisciplinary study and team teaching. There are many opportunities for you to relate this unit to other subjects. The measurements that students make open up opportunities to discuss the mathematical concepts of variation, normal distributions, and significant differences. The genetic code is a wonderful way to introduce permutations and more simply deal with very large numbers. Of course, Mendelian genetics revolves around ratios. Language arts and social studies can be emphasized in writing and discussing controversial issues such as genetic cloning, genetic testing, and environmental mutagens. Health can be emphasized in discussions of genetic disorders and genetic counseling.
The genetics unit is inquiry based and provides abundant hands-on activities. The learning gains and the retention by the students are much greater than is accomplished with a traditional text approach. The activities in this unit are especially important to help students conceptualize the cellular and molecular mechanisms of genetics. After all, making a molecular model of DNA similar to the ones your students will make resulted in Nobel Prizes for James Watson and Francis Crick! The activities also are helpful in presenting the quantitative aspects of genetics. The activities in this unit offer opportunities for creativity. They are not difficult, and the materials required are common items.
We are confident that you and your students will enjoy this unit and that your students will learn more about genetics than you or I did when we were in high school.
H. Craig Heller
Chair, Department of Biological Sciences, Stanford University