National STEM education reform efforts call for increased emphasis on science practices, such as modeling. We describe an activity where students read a scientific blog post relating human gametogenesis to disease and then during class develop a model explaining why defects in meiotic machinery cause this disease. This interactive activity was implemented in two sections of an introductory biology course, each exceeding 150 students. Overall, students responded positively to the activity, and based on follow-up exam questions addressing the main learning goals of the modeling activity, about 70 percent of students mastered the learning objectives associated with the modeling activity.
National STEM reform aims to align teaching science with scientific practices and shift focus from memorization of details to understanding of big ideas (NGSS Lead States, 2013a,b; AAAS, 2011), with the goal of educating the next generation to be informed citizens who have an understanding of and appreciation for science. Moreover, learning about these practices engages students with new and current advances in science (Passmore et al., 2014). A key science practice is the development and use of models. Scientific models are simplified representations of complex biological concepts that explain a phenomenon or process both descriptively (how) and mechanistically (why). Scientific models are used as tools for making sense of phenomena and processes (Passmore et al., 2014). Models are powerful scientific tools because they allow scientists to make predictions that can be tested by comparing the predictions generated from the model with observations and experimental data. This provides empirical validation of ideas in the model (Schwarz et al., 2009).
Historically, science instruction has focused on memorizing the stages of meiosis, but Vision and Change calls for a focus on learning big ideas, such as information flow (AAAS, 2011). Studies have shown that incorporating interactive modeling lessons into classrooms increases student performance on conceptual questions and increases student confidence in their understanding of meiosis (Wright & Newman, 2011; Clark & Mathis, 2000; Kreiser & Hairston, 2007). These studies were from classrooms significantly smaller than the average class sizes for introductory STEM courses at our institution. Here we present an in-class modeling activity in a classroom containing more than 225 students where students develop a model to describe the gametogenesis of a fictional organism. During this activity, students collaborate to construct a model that mechanistically describes a biological phenomenon and use their model to predict outcomes. In our introductory biology course, students completed this activity toward the end of our “cell cycle module.” One big-picture goal of this module is understanding the flow of genetic information during cellular processes. This module consisted of pre-class readings, homework, and lectures on the topics of the roles of cell division, regulation of the cell cycle, eukaryotic chromosomes, mitosis, and meiosis. The strategy of the activity is to help students understand information flow, and it is focused on the mechanism of chromosome sorting.
Students must then use their understanding of information flow to make predictions and connect how failures in meiotic mechanisms might cause human disease. One important aspect of this activity is that there are multiple correct outcomes, so that simple memorization is not sufficient for students to develop a plausible model. Having an activity with multiple outcomes allows students to think “outside of the box” and make their own predictions that they can support using their model, reflecting aspects of how real science is conducted.
We created this activity for students in an introductory biology course for STEM majors at Michigan State University, a land-grant R1 university located in the Midwest. However, with minor modifications the activity is likely appropriate for introductory biology classes in a variety of undergraduate and high-school settings. This activity was implemented in two sections of the course with enrollments of 152 and 229. This 3-credit course met twice a week for 80-minute class periods. The majority of students (more than 70 percent) typically take this course during either freshman or sophomore year. Each section had a teaching team made up of two instructors, two graduate teaching assistants, and three undergraduate learning assistants.
The content goals of this activity are for students to:
Use their knowledge of human gametogenesis to model the process of meiosis in a fictional organism.
Follow chromosomal sorting throughout meiosis I and meiosis II during normal and abnormal gametogenesis.
Describe how alterations in either meiosis I or meiosis II could affect gametes.
Explain why alterations in meiosis can result in disease.
The science practices goals of this activity are for students to:
Develop a scientific model:
represent key aspects of meiosis visually.
describe mechanisms in their model by writing cause-and-effect statements.
Communicate what they have learned:
present their model to the class via a 5-minute oral presentation, displaying their model using a document camera.
compare and contrast their model to models presented by other groups.
Apply what they have learned:
predict how scientific data from a fluorescence-activated cell sorting (FACS) experiment may look given their specific model.
relate this phenomenon to other biological processes, such as mitosis.
To meet these objectives, students should already have a basic understanding of mitosis and meiosis. These content and scientific practice goals could easily be adapted to meet Next Generation Standards if implemented in a high school setting.
Representative pre-class homework questions (Figure 1)
Blog article on chromosomal segregation in oocytes: Institute of Molecular Biotechnology, “Molecular glue controls chromosome segregation in oocytes,” ScienceDaily (November 27, 2013), http://www.sciencedaily.com/releases/2013/11/131127122309.htm
Meiosis packet (Figure 2):
8 pipe cleaners of 2 different colors, 4 per color
Instructions (Figure 3A)
Modeling scaffold sheet (Figure 3B)
Model extension exercise (Figure 4)
We created this activity so students could experience scientific modeling of meiosis with a hands-on component. To represent the DNA of fictitious organism Sparticus biologicus, we chose to use pipe cleaners of various colors. Each pipe cleaner represents one single-stranded DNA molecule, and each color represents DNA from one parent, either maternal or paternal. We chose to have a pipe cleaner represent a single strand of DNA because some of the common misconceptions students have is that replicated chromosomes are no longer double-stranded DNA and no longer contain DNA from only one parent (Newman et al., 2012). We thought it was important for students to assemble the DNA helices themselves to help students confront these misconceptions (Newman et al., 2012). In our model, our organism had only one chromosome pair. Therefore, each “meiosis packet” contained eight pipe cleaners, four of each color (Figure 2). It is possible to modify this activity to use more chromosomes and chromosomes of varying lengths. We chose to represent cohesin, a protein complex that holds sister chromatids together (Klein et al., 1999), as beads. Although cutting the pipe cleaners and assembling the “meiosis packets” was time consuming, the packets can easily be reused.
Pre-class homework questions
Scientific Blog to be read before class
Introduction (5 minutes)
Boxes 1–3 (15 minutes)
Presentations and Discussion (2–3 groups) (10 minutes)
Boxes 4–6 (15 minutes)
Presentations and Discussion (2–3 groups) (15 minutes)
Activity wrap up and model extensions (20 minutes)
Prior to class, students read the scientific blog and completed a series of homework questions related to topics from class using the online McGraw Hill Connect platform. Figure 1 is a representative of the some of the pre-class questions students had to answer. At the start of class, we had students self-assemble into groups of three while we passed out the meiosis packets (Figure 2), instructions (Figure 3 top), and scaffold sheets (Figure 3 bottom) (Kang et al., 2014). Students were instructed to use what they have learned in this course to develop a meiosis model explaining why abnormal cohesin affects gamete production, as well as the importance of chromosome sorting during meiosis.
Following this brief introduction, students worked on boxes 1–3 of the activity. In their groups, students used pipe cleaners to model the structure of double-stranded DNA and drew the chromosomes of Sparticus biologicus. Students modeled the chromosomes going through prophase I and drew this in box 3. During this time, the instructors, graduate teaching assistants, and undergraduate learning assistants (the teaching team) walked around from group to group facilitating discussion of the models and answering any questions students may have had. For specific questions, the teaching team followed a Socratic dialog by responding with open-ended questions. If students did not know how to start, we referred them to resources such as their textbook and the pre-class assignment. The teaching team also asked groups to present their work-in-progress model. After about 15 minutes, we had our first round of student presentations, where two to three groups presented their models. Presenting groups projected their model using a document camera so the entire class could see their model, and then used their model to explain what is happening to Sparticus biologicus during prophase I, and to explain what is happening to the type and the amount of genetic material in this stage. During each set of presentations, groups were asked to think about and take notes on:
one thing that their model and the presented model have in common.
one thing from their model that could be added to the presented model to improve it.
one thing from the presented model that can be added to their model to improve it.
Additionally, for each group that presented, we asked for feedback or questions from the audience, and the instructors facilitated a discussion. As this is a team-taught course, the two instructors took turns leading and facilitating discussions throughout the modeling exercise. After the first set of presentations, students continued working on their activity by completing boxes 4–6.
The second half of the modeling activity was centered on applying the blog that was assigned as pre-class reading and using the model to determine the effects on chromosomal segregation. As before, each member of the teaching team walked around answering questions and facilitating discussions in groups. For boxes 4 and 5, students used evidence from their model to explain how and why chromosomes sort as Sparticus biologicus progresses from prophase I to telophase I, and continued following the genetic information through meiosis II. In box 6, students used their understanding of the underlying mechanisms in meiosis to write cause-and-effect statements to explain the resultant gametes they drew in box 5. This part of the model tied back to the assigned reading and allowed students to explore at which point(s) during meiosis cohesin may have malfunctioned. This part of the model made the second set of presentations and the resultant class discussion more in-depth and stimulating, as cohesin can malfunction during either meiosis I or meiosis II (Klein et al., 1999). When selecting groups to present for the second set of student presentations, we tried to find groups that had different outcomes of gametes (see Figure 6). An example of a group's model is shown in Figure 5.
The presenting groups were asked to use their models to explain what happened to the gametes produced by Sparticus biologicus and explain, using evidence from the blog and their models, at which point cohesin was defective. During the presentations, students were quick to realize that the resultant gametes of Sparticus biologicus can be different depending on which stage (meiosis I or meiosis II) had the cohesin malfunction. The instructors then prompted a class discussion with the following clicker question:
Model Extension 1: An individual has Down syndrome (trisomy 21). Based on what you know about meiosis, the cell cycle, and the cohesin blog, which of the following is likely?
Homologous pair (#21) in the gamete failed to separate during meiosis I.
Sister chromatids (#21) failed to separate during meiosis II.
Cohesin was not able to be broken down by separase.
Three copies of chromosome 21 were made in S phase.
As this was a class discussion, we asked for student volunteers to explain their answer choices of the model extension. This led to a fruitful discourse about human gametogenesis and diseases caused by chromosomal segregation problems. Once it was established, using the combination of the scientific blog and the predictions students made with their models, that options a, b, and c are each likely, the students moved on to the second model extension (Figure 4).
During the second model extension, students applied what they have learned from the activity and used their models to predict results from a fluorescence-activated cell sorting (FACS) experiment. In a FACS experiment, Hoechst33258 dye that binds DNA and fluoresces blue is used (Bonner et al., 1972). Cells in a population are then sorted into different categories based on the level of fluorescence in each cell (Bonner et al., 1972). In their groups students were asked to use their models to predict what populations of cells may look like if Sparticus biologicus was actively undergoing normal mitosis, normal meiosis, and meiosis with abnormal cohesin, and represent these graphically (Figure 4). Following this was a discussion led by one of the instructors during which groups were asked to volunteer to draw their predicted results on a tablet computer (the instructional computer, although a document camera, overhead projector, or chalkboard may also be used), for each of the questions in Figure 4. Here, students were challenged to “think like scientists” and hypothesize why the results of the FACS would differ for cells in different stages of mitosis and meiosis, based on their DNA content. Examples of possible outcomes are shown in Figure 6.
Following the model extension discussions, students turned in their scaffolds that contain their models and their meiosis packets. In our class, each groups’ instruction sheet listed a group number. Each group member joined that group in our institute's learning management system, Desire2Learn (D2L), prior to submitting their completed modeling assignment. At the end of class, one group member took a picture of their completed scaffold sheet using their cell phone and uploaded it to the group's dropbox in D2L. The grading was then completed by the instructional team using the rubric function in D2L. Graders viewed the image of the student's completed scaffold sheet (Figures 5 and 7). and selected performance levels in the rubric (Figure 8). They also provided written, individual feedback in the feedback box (Figure 7). Each group was able to view the rubric and receive feedback on their work after the grades were submitted.
Assessment of the Model
This model is meant to function as formative assessment for students. Each group's model is graded using a rubric focused mostly on completion, but with a small component related to the plausibility of the model to provide students with feedback on the strength of their model (Figure 8). This low-stakes approach keeps groups focused on the modeling process rather than trying to find a correct answer.
Additionally, every group receives written feedback specific to their model (see Figure 5 for an example). To evaluate student learning at the end of the cell division module in our course, the meiosis model learning objectives were used to develop a summative short-answer question worth 1/5 of the exam. The exam was a combination of 30 multiple-choice questions (each worth 2 points) and two short-answer questions covering the topics of matter and energy transformations in photosynthesis and meiosis (worth a total of 20 points). The short-answer question based on the meiosis model was split into two parts. The first part assessed the ability of students to read and interpret scientific data represented in a FACS experiment, which was part of the model extension (Figure 6). The second part assessed the ability of the students to trace chromosomal DNA flow through mitosis and/or meiosis. Overall, the average on the exam, which consisted of both multiple choice and free-response questions, was 68 percent. The average grade on the meiosis short answer question was 72 percent, and the average grade on the photosynthesis question was 65 percent.
Overall students responded positively during this in-class exercise. However, there were some concepts that students struggled with. For example, some students did not make the connection that each pipe cleaner represented ssDNA. As such, they completed the activity with the misconception that there was twice as much DNA in Sparticus biologicus as there should have been. Additionally, there was some initial confusion and concern among the students when they realized that there were multiple, correct outcomes to the activity (i.e., that one group may have modeled the DNA distribution differently than another group, and both were valid mechanisms for meiosis-related disease). This confusion was alleviated after the second round of student presentations, followed by instructor-guided discussion.
This modeling activity is one example of five total modeling exercises in our course. In addition to this modeling exercise, the other ones within our course include the following core concepts: (1) protein structure, (2) matter and energy transformation, (3) stem cell differentiation, and (4) cell signaling and cancer. Of 190 total comments on the end-of-semester course evaluation from the larger section, 22 percent of the comments were about the modeling activities, and of these, 93 percent were positive. For the smaller section, we had a total of 124 comments, with 26 percent of those comments being about the modeling activities, of which 97 percent were positive. Examples of student comments include:
“… the modeling activities were the most helpful for me. It allowed more in-depth analysis of the things we were learning which made it easier to understand the basic concepts …”
“… modeling activities [were the most helpful] because they helped visualize the process …”
“The modeling activities were the most helpful to my learning because they took the most difficult processes and broke them down so it was easy to develop an intuitive understand[ing] of what was going on …”
“… modeling activities allowed us to connect our class knowledge to real issues and problem solve as many scientist[s] are doing right now …”
Our meiosis model allows students to use a hands-on method to develop an understanding of the mechanism of meiosis using a fictitious organism. Students then apply this to human gametogenesis and begin to explore how and why chromosomal segregation problems can cause disease-related problems in offspring. This activity employs active learning and allows students to participate in the scientific practices of modeling and of communicating their ideas. Moreover, reading a scientific blog helps students connect their classroom knowledge to how real scientific studies are often presented in the popular media. Our overall goals were to combine skill development and scientific content to help train the next generation of students to be scientifically literate and to think critically early on in their careers. Overall, this activity is a great addition to undergraduate and advanced high-school biology courses.