Thursday’s Lesson

Exploring Genetics with BioLogica™

By Paul Horwitz

Of all the topics in the middle and high school life science curricula, genetics is probably the hardest to teach and to learn. The reasons for this are obvious: genes, proteins, chromosomes, and all the rest of the machinery responsible for genetic phenomena are not visible to the naked eye, nor is there any obvious connection between them and the observable phenotypic variations to which they give rise. In fact, the evidence for that connection is indirect and depends on statistical and probabilistic reasoning that is itself unfamiliar to most students. No wonder so many students, faced with the ubiquitous Punnett square, manage to master the mechanical process of entering letters into each cell of the matrix without ever understanding how that matrix represents meiosis and fertilization, or what it has to do with predicting the statistical outcome of random processes such as chromosome segregation and gamete selection.

Nor are these students helped much by invoking the name and recounting the story of Gregor Mendel. Mendel discovered the outlines of the genetic basis of life by observing variation in multiple generations of plants, but it took him eight years to do it and he was a genius. Surely it is asking a great deal for an adolescent to recapitulate the process in a matter of days!

Figure 1. A view of the meiosis level of BioLogica. The dragons in the right and left panels are the father and mother, respectively, of the dragon in the middle, whose phenotype is determined by the genes it received from its parents.

BioLogica™ (and its predecessor program, GenScope™, which has been rendered obsolete by the Mac OS X operating system) enables us to approach the problem of teaching genetics from the other direction. Instead of starting with the data and working backwards, as Mendel did, BioLogica operationalizes Mendel’s famous laws in the form of a manipulable computer model; the software allows students to experiment with the model and work out its consequences for themselves. Admittedly, this pedagogical approach does not capture the subtle and multilevel reasoning that led to the original discovery, but that lofty goal is probably unattainable for most beginning students and can arguably be postponed until later in their biology education.

Exploring genetics

The activity, called “Exploring Genetics,” is adapted from a five-day project entitled “A Dragon Named Meiosis” developed by Beat Schwendimann, a fellow of the Technology Enhanced Learning in Science (TELS) Center, in which the Concord Consortium is a partner.

Go to www.concord.org/resources to download an exploratory activity based on BioLogica.¹

The activity was designed to last approximately one class period, but is broken into three independent parts so that it can be revisited without becoming repetitious. No previous experience with BioLogica is assumed, but we recommend that students be introduced to Mendelian genetics prior to tackling the activity.

Figure 2. A view of a dragon’s chromosomes. When a gene is changed from one allele to another, the image of the corresponding dragon changes in accordance with Mendel’s Laws.

After an introductory screen explaining its purpose, the activity presents a standard BioLogica model consisting of two dragons²—a male and a female—and two sets of chromosomes, one for each dragon.

Have students explore the model by changing genes in order to determine the rules governing dragon traits: the presence or absence of horns or wings, tail shape, number of legs, color, and so forth. Many of these traits are governed by the interaction of dominant and recessive alleles as prescribed by Mendel’s First Law, while others are incompletely dominant, X-linked, and polygenic. Beware: one of the color genes is a recessive lethal—you could kill your dragon!

Challenge: make (particular) dragon babies

After responding to a few embedded questions about the model, students run germ cells from a male and a female dragon through meiosis, examine the resulting gametes under a virtual “magnifying glass” to determine which alleles they carry, select one gamete from each dragon, and pair them in a simulated fertilization process that results in a zygote and a full-fledged baby dragon. Because the phenotype of the offspring is determined by the particular allelic combinations it carries, one can ensure the presence of any trait for which the appropriate alleles are present in the parental genotypes by selecting gametes judiciously. And that’s the challenge: students must put into practice the phenotype-to-genotype rules they learned earlier.

The final three screens in the activity contain challenges of increasing difficulty:

• Make a winged dragon.
• Make a dragon with four legs.

And the Platinum challenge:

• Make a green dragon with a plain tail.

Efficiency in choosing gametes is rewarded. When a student exits the activity, we report on how many attempts were made on each challenge, and how often the gametes were inspected to determine their alleles.

What’s missing?

Detailed though this activity is, it still leaves out several crucial aspects of the inheritance of traits through sexual reproduction: the essential randomness of the process and the statistical analysis made necessary by that randomness. In the BioLogica model, students have complete control over chromosome segregation and gamete selection prior to fertilization³ and the parent organisms are pre-selected. In nature, of course, neither chromosome segregation nor gamete selection can be controlled, and mate selection has a significant random component. Consequently, the genotype of any particular offspring can only be predicted statistically. In dealing with the underlying causes for differences between offspring of the same parents, this activity offers an explanation for the non-uniform distribution of phenotypic traits that formed the basis for Mendel’s laws. It does not take the next step of demonstrating how those laws actually emerge from the model.

BioLogica includes a pedigree level that is designed to help students make the intellectual leap between the randomness of the underlying processes and the statistical patterns that emerge from their repeated application. And in BioLogica’s population level, simulated organisms roam around the screen, mating randomly and surviving differentially, subject to selective pressures that are phenotypically determined.

From Punnett squares on paper to changing dragons’ genes in a model-based environment, students can learn about genetics one allele at a time—even if you can’t produce multiple generations of Mendel’s pea plants in your classroom!

Paul Horwitz (phorwitz@concord.org) is Co-Principal Investigator on the TELS project and the developer of GenScope, the precursor to BioLogica.