Genetics Teaching Vignettes: Middle School
Genetics at the Middle School Level: Toothpick Fish
List of Classroom Activities:
The Design-A-Kid Activity reinforces basic genetics concepts such as dominant vs. recessive, homozygous vs. heterozygous, genotype vs. phenotype, incomplete vs. complete dominance, and also provides a graphic demonstration of genetic assortment and the phenotypic variation that it leads to. Students determine the phenotype of their "offspring" or "kid" by randomly choosing alleles from mock heterozygous parents (determined by coin tosses). Students compare drawings of their kid with other studentsí kids and observe that no two kids look alike, providing an illustration of how phenotypic variation arises.
In the Toothpick Fish Activity, used toward the end of the genetics unit, students explore interactions between genes and environment for a population of "fish" (colored toothpicks). Students learn about the relationships between many different parts of fish life: genes, traits, variation, survival, and reproduction. The activity is a simulation and models the way fish and other organisms live in nature. This activity should be undertaken only after students have a clear understanding of dominant and recessive genes, genotype and phenotype, and understand how to use Punnett Squares.
In Toothpick Fish, the toothpicks represent genes that control one fish trait: skin color. Some of the genes are dominant and others are recessive. For example, the green gene is dominant to all the other color genes. Initially, students work out what combinations of toothpicks (genotype) will result in what colors of fish (phenotype).
A population of fish (24 colored toothpicks) in a "stream" (a plastic petri dish) is then observed as events impact their environment. Changes in the genetic-makeup of the population over several generations are charted. The environmental events impacting the fish gene pool are ones that could happen in a real stream. For example, students examine what happens to the predominantly green fish population when pollutants added to the stream kill the green algae that provides camouflage for the green fish.
In a related writing exercise, students write about other organisms and how their characters may or may not be the result of selection.
To extend the evolution and environment theme, another scenario that can be presented is the case of the peppered moth, a famous example of how a changing environmental factor, worsening air pollution, can act as a strong selective force and alter a population, in this case, the color of the local moth population in early industrial England. Althoughf the peppered moth scenario is not presented in Merrill Life Science, it is described in many high school genetics textbooks. Another source of background information on the peppered moth, complete with a low-cost classroom activity, can be found online (see above under Instructional Materials).
Additional genetics classroom activities can be drawn from the student biotechnology magazine Your World/Our World. The Human Genome Project section in Merrill Life Science can be supplemented by discussion of genetics-related ethical issues such as those presented in the student booklet, Your Genes, Your Choices, or recent genetics-related articles in the media, such as Time Magazineís Future of Medicine issue (January 11, 1999). The history of science and scientist role models, including women and minority scientists, are introduced by reading aloud to students for 10 minutes each day about science "heroes" such as Gregor Mendel and Barbara McClintock. Marvels of Science contains a number of engaging, fictionalized accounts of famous scientistsí discoveries and Eureka moments. A good soucebook for stories on women scientists is The Remarkable Lives of 100 Women Healers and Scientists.
Genetics Concepts and Essential Learnings:
Last updated 02/03/03