NIH Public Access Author Manuscript Sci Teach. Author manuscript; available in PMC 2014 October 14.

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Published in final edited form as: Sci Teach. 2013 December ; 80(9): 37–43.

WHAT MAKES US TICK…TOCK?: USING FRUIT FLIES TO STUDY CIRCADIAN RHYTHMS Kristen Talbot and Barbara Hug Kristen Talbot ([email protected]) is a high school science teacher and former Masters in Curriculum and Education graduate student, and Barbara Hug ([email protected]) is a clinical associate professor in the Department of Curriculum and Instruction, at the University of Illinois at Urbana-Champaign

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Teachers often ask: How can I engage my students in the study of “real” science? The answer can be found in the National Research Council’s A Framework for K–12 Science Education: Practices, Crosscutting Concepts, and Core Ideas (NRC 2012). This framework calls for a new approach to science education and is the basis for the Next Generation Science Standards (NGSS) (NGSS Lead States 2013). It emphasizes the need for stronger collaboration within the scientific community to develop curricula that address the core ideas, scientific practices, and crosscutting concepts for all students. Project NEURON has developed a curriculum unit titled, “What makes me tick…tock? Circadian rhythms, genetics, and health,” that combines scientific practices identified in the Framework and NGSS (Figure 1, p. 38); core biological ideas, such as Genetics and Animal Behavior; and crosscutting concepts, including Cause and Effect, Structure and Function, and System Models. Unit materials are available free online (see “On the web”). This article gives an overview of the unit, then describes in detail one of its eight lessons.

Unit overview

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The first lesson asks students to draw connections between the science of circadian rhythms and their own lives. The students discuss how their behavior and moods can be affected by their sleep-wake cycle. In Lesson 2, students focus on how environment and genetic mutations can affect the sleep-wake cycle. In Lessons 3 and 4, they investigate how specific genetic mutations can lead to physiological and behavioral changes. In Lesson 5, students investigate light intensity in their schools and ponder how humans’ exposure to light can affect circadian rhythms. In Lesson 6, students examine conditions that can disrupt humans’ circadian rhythms and then report on the dangers of this phenomenon. In Lesson 7, students explore epigenetics and how environment and lifestyle choices can influence not only their own circadian rhythms but also their offspring’s rhythms. Finally, in Lesson 8, students create a proposal for school administrators that makes a case for when the

Copyright © 2013, National Science Teachers Association (NSTA). On the web NetLogo simulation software: http://ccl.northwestern.edu/netlogo Project NEURON lesson materials and student assessment guides: http://neuron.illinois.edu

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school day should begin. The students use their findings from the unit’s activities as evidence and reasoning to back up their proposal. Figure 2 (p. 39) provides an overview of the “What makes me tick…tock?” unit. A closer look at Lesson 2

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Lesson 2, “Why do scientists study fruit flies to understand what makes us tick?” demonstrates the unit’s integration of scientific practices, crosscutting concepts, and core ideas. This lesson uses NetLogo, a free software program available online (see “On the web”). NetLogo allows curriculum developers and teachers to create simulations for students to develop, test, and revise scientific models, a key scientific practice. The simulation of fruit fly behavior is based on authentic scientific data generated in a basic research science laboratory (Majercak et al. 1999). This eliminates the need to acquire and maintain live fruit flies in the classroom. The first simulation explores how the fruit flies’ activity levels (phenotype) are directly affected by the amount of light and temperature (environment). The second simulation demonstrates how the fruit flies’ activity levels are affected by the genotype of the flies. Throughout the lesson, students develop, use, and revise models explaining these phenomena. By observing how environment or genotype can cause a specific phenotype, students collect data to modify their models and explanations. This lesson also connects circadian rhythm studies in flies to humans. Students are asked to discuss how their genetics and environment can affect their circadian rhythms and daily activities. Focusing on the scientific practice: Developing and using models

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Two key scientific practices are Asking Questions and Developing and Using Models. These practices are essential to understanding how scientific work is done. In the “What makes me tick…tock?” unit, many lessons are designed so students can gain more experience with these scientific practices. Specifically, students ask questions and develop initial models of what sleep-wake cycles are and how they function in Lessons 1 and 2. These initial models serve as a baseline for what students believe will happen to an organism’s circadian rhythm when environmental cues are modified (e.g., changing light and temperature). In Lesson 2, students revise these models to develop more sophisticated hypotheses regarding circadian rhythms. They do this by gathering data from the activity levels of a specific model organism (i.e., Drosophila melanogaster) in response to a specific entrainment schedule (light-dark cycle) or in response to changes in warmer or colder room temperatures. When students develop models based on the effects of temperature change on circadian rhythms, they frequently relate humans’ responses to temperature to the fruit flies’ responses. Some students initially believe that the flies will be more active when it is warm because they, as humans, are more active in warm weather than in cold. However, other students say they shiver in the cold, so they believe the flies will be more active when it is cold in an effort to stay warm. These differences show the importance of developing a model that corresponds to the first step of Figure 3. In this initial phase, students bring their own experiences and prior scientific knowledge into developing a model. These are used to generate subsequent testable hypotheses on how the environment affects the flies’ and other

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organisms’ circadian rhythms. This process also allows teachers to assess where students are in their understanding of ideas and the need to address possible misconceptions.

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Once students generate testable hypotheses, they use the NetLogo simulation to collect data that either support or refute their initial hypotheses. Each simulation data point corresponds to the fruit flies’ activity at a specific 24-hour time point under certain experimental conditions. Students graph their collected data, determining the highest and lowest levels of the flies’ activity. Once the data is graphed, students are able to analyze it and draw conclusions on how entrainment at a known hour pattern of a light-dark cycle (14:10, 12:12, 10:14, and 8:16) affects flies’ activity at room temperature, 25°C (Figure 4). Using findings from this first investigation, students develop an explanation about how light can impact the specific behavior of an organism. Students continue to explore additional variables that influence circadian rhythms by looking at one entrainment schedule—12:12 light-dark cycle —and measuring fly activity levels at different temperatures: 18°C, 25°C, or 29°C (Figure 4). Again, students graph their collected data points to draw conclusions about how temperature affects the flies’ activity in a 24-hour period.

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Teachers should encourage students to explain what is reflected in their graphed data and how it relates to their models. This may result in students revising and strengthening their initial models. Depending on how many data points are collected and plotted on their graphs, students’ interpretations of the flies’ activity levels can be vastly different, even when testing a similar hypothesis. For example, one teacher reported that because students did not collect enough data points, their flies appeared to be active at only one time period during the 24-hour day. However, in the class discussion, students were reminded that because fruit flies are crepuscular (active at dawn and dusk, or twice during the 24-hour day) their current graphs conflicted with documented fruit fly behavior. As a result, the students concluded they needed to collect additional data points to more accurately capture and represent how entrainment schedule affected flies’ activity levels.

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Students then examined how individuals can have variation in their circadian rhythms. This leads to a discussion on the role of genetics in circadian rhythms and the idea that a genetic mutation can change one’s “tick.” Based on their findings from the first NetLego simulation, students then revise the original model or create a new one to factor the role of genetics in circadian rhythms. One of the genes that plays a major role in regulating fruit flies’ biological clocks is the period (per) gene. These homologs are found in both rats and humans. Scientists frequently study mutations of a model organism’s gene to investigate a scientific phenomenon, such as the biological clock. A key difference between this NetLogo simulation and the previous simulation is that all of the flies are kept at the same temperature and entrained in a 6:18 light-dark cycle for four days. Students collect data on the fourth day (Figure 5). Students can also collect data from the fifth day, when the flies are placed in complete darkness. Students first compare data between the different fly mutations for either Day 4 or Day 5 over a 24-hour period. The activity can be extended by collecting data over the 24-hour time period for both Day 4 and Day 5 and comparing the flies’ activity levels on those two days, as well as across the different fly mutations. Students choose which gene to test (perA, perB,

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or perG) and which day(s) to collect data from, then run the simulation, record the data, and document the flies’ activity levels at various time points in a 24-hour day via a line graph.

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Students use the graphs to conclude how each mutation affects the flies’ circadian rhythms. The mutation may, or may not, cause the flies to diverge from their natural crepuscular circadian rhythm. In groups, students discuss how the different mutations changed the flies’ activity levels and how these gene mutations might manifest in humans: If a person had a per gene mutation, how would his behavior change? How might a mutation affect his daily life? The students conclude that while this may be difficult to assess in humans, scientists can isolate genetic mutations in a model organism and then analyze the resulting behavior based on the specific mutation. This activity shows students how scientists frequently revise and refine their models through data collection and analysis. Assessing student learning

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These NetLogo activities provide a variety of informal assessments that offer a rich set of evaluations. This lesson plan features many discussion questions suitable for partner, smallgroup, and whole-class discussions. These discussions can be monitored and used to evaluate student learning. Informal presentations of Netlogo simulation data also can be used as performance assessments at different stages of the investigation. Throughout the series of activities, student models can be evaluated based on the following criteria: (1) the explanatory power of the model and (2) the predictive power of the model (Figure 6). Other criteria (e.g., model accuracy and use of data) could be added to the rubric based on class discussion of what makes a strong model. For lesson materials and assessment guides for students’ performance, see “On the web.”

Feedback from the field

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Five teachers from our professional development community have used this lesson. Notably, two teachers from vastly different school communities have had repeated success with the unit in their classrooms. One teacher is in a small urban community with 53% of students identified as low-income, while the other teaches in a suburban school with 15% of students identified as low income (Illinois State Board of Education 2012). Both say that the simulation technology allows their students to easily connect the flies’ circadian rhythms with their own. The teacher from the small urban community notes: “It [the simulation] models a real-life situation and fits into the parameters of the classroom. Since I cannot have live fruit fly entrainment experiments in the classroom, NetLogo is more practical and provides the same experience.” Our teachers use small groups of students to complete these activities. They say this arrangement encourages rich discussions and helps teachers evaluate which concepts students understand well and which need more attention. The teachers also say the simulation helps students observe the circadian rhythm in a more scientifically investigative way, as opposed to anecdotal discussions. The activities are worth-while because students

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engage in scientific practices aligned with disciplinary core ideas and crosscutting concepts, which lend themselves to both informal and formal assessments.

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Acknowledgments The development of the curriculum reported in this publication was supported by the Office of the Director, National Institutes of Health, under Award Number R25OD011144. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

References Illinois State Board of Education. Interactive Report Card. 2012. http://iirc.niu.edu Majercak J, Sidote D, Hardin PE, Edery I. How a circadian clock adapts to seasonal decreases in temperature and day length. Neuron. 1999; 24(1):219–230. [PubMed: 10677039] National Research Council (NRC). A Framework for K–12 science education: Practices, crosscutting concepts, and core ideas. National Academies Press; Washington, DC: 2012. NGSS Lead States. Next Generation Science Standards: For states, by states. National Academies Press; Washington, DC: 2013.

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FIGURE 1. Alignment with the Next Generation Science Standards

These lessons align with the following NGSS, among others.

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FIGURE 2. Unit Overview: “What makes us tick…tock?”

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NIH-PA Author Manuscript FIGURE 3.

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During Lesson 2, students use their initial ideas to create models. Once they test their models, students collect data, analyze their data, and develop explanations to revise their models. Students then discuss how genetic mutations or changes in their environment can affect their sleep-wake cycles.

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NIH-PA Author Manuscript FIGURE 4.

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Below are the NetLogo simulations of five flies’ activity levels entrained on a 12:12 lightdark cycle at 25°C (left) and flies entrained on a 12:12 light-dark cycle at 29°C (right). The flies’ paths are shown as trails behind them, with their average total activity represented in ticks per second. The gray slider bar across the top of the window allows students to adjust how fast or slow the flies move, speeding up the data collection process. The “average total distance” represents the average activity for the five flies at a specific time point. In the examples below the time point is hour 0.

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NIH-PA Author Manuscript FIGURE 5.

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The NetLogo simulation of the per gene mutations allows students to examine what happens to the fruit flies’ activity levels when one of four gene mutations is introduced. The data collected on Day 4 shows an average total activity of 322.96 ticks at time point 1.04 (left). With the same mutation, but with data collected at Day 5, the average total activity was 1427.84 ticks for the five fruit flies (right).

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FIGURE 6. Examples of rubrics for the lesson on developing models

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WHAT MAKES US TICK…TOCK?: USING FRUIT FLIES TO STUDY CIRCADIAN RHYTHMS.

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