“Cootie Genetics” is a hands-on, inquiry-based activity that enables students to learn the Mendelian laws of inheritance and gain an understanding of genetics principles and terminology. The activity begins with two true-breeding Cooties of the same species that exhibit five observable trait differences. Students observe the retention or loss of traits among first-generation heterozygotes, hypothesize what happened to these traits, and design an experiment to test their hypotheses by mating the first-generation Cooties. With the second generation, Mendel’s principles of segregation and independent assortment of alleles are observed; dominant and recessive traits and tools students need to construct Punnett squares are apparent.
Current pedagogy in the biological sciences is focused on inquiry-based STEM activities, which encourage students to be interactive, engaged, and capable of drawing connections between the classroom and the outside world. To this end, we have developed “Cootie Genetics,” which enables students to use Hasbro-brand Cooties toys as a tool for predicting, simulating, and visualizing three generations that exhibit traits in accordance with the mathematical patterns of the Mendelian laws of inheritance. Drawn to the familiarity of a common childhood toy, students quickly become engaged in the experiment, which teaches them the practical tools of data collection and analysis using the scientific method and ultimately leads to understanding the laws of inheritance.
Teaching middle and high school science standards requires understanding of reproduction and inheritance, as addressed in the Life Science Standards (National Research Council, 1996). In the past, these concepts were introduced during high school biology courses. The second draft of the Next Generation Science Standards (cited throughout this article, in parentheses after relevant sections) indicates that teachers will need to introduce such concepts at an earlier stage.
Introducing basic subjects, such as genetics, earlier in school allows students more time and practice to gain familiarity with the concepts of heredity and inheritance (Eshach & Fried, 2005). If genetics and its accompanying vernacular can be introduced in an effective way to promote early understanding, students will have a strong foundation upon which they can build a comprehensive understanding of more difficult fields such as molecular genetics, ecology, and evolutionary biology.
It is generally accepted that scientific inquiry in the classroom is “at the heart of the science and science learning” (Eshach & Fried, 2005). Ideally, the teaching of science should reflect the process used by the original scientific researchers (allowing individuals to come to their own conclusions, reflecting those of the original researcher). Scientific inquiry is a theme that runs through all grade levels of the science standards. In this investigation, students will learn about the molecular biology of heredity by doing what Mendel did: breeding an organism, collecting data on the offspring, and analyzing the trends in that data.
Teaching Genetics Using Scientific Inquiry
The Jr. Biotech Project at the University of Arizona developed Cootie Genetics, which allows students to learn the basic ideas of Mendelian genetics with no prior introduction. Using computer simulations of two fictional, distinct, pure-breeding populations, students “breed” Cooties, predict the outcome of the offspring and the ratio of their five visible traits, and examine the statistical relationships among the various hybrid offspring. Teachers give students the pertinent information to establish simple hypotheses. Classroom discussion allows students to design multiple ways to test their hypotheses, and to discuss the pros and cons of each. The genetics vocabulary is introduced after learning the concepts, allowing time to thoroughly understand the central theories before convoluting them with a new and complex vocabulary.
Cootie Genetics is a hands-on, inquiry-based activity that enables students to learn the Mendelian laws of inheritance by conducting experiments similar to those famously pioneered by Gregor Mendel. Using Hasbro-brand Cooties toys, students simulate Mendel’s experiments in order to gain a practical and enduring understanding of foundational genetics principles and terminology. The activity begins with two true-breeding Cooties of the same species that exhibit five observable trait differences between the two populations. Students “breed” members of the two populations and observe the retention or loss of traits among first-generation heterozygotes. Using the scientific method, students then hypothesize what happened to these traits and design an experiment to test their hypotheses by mating the first-generation Cooties. With the production of 40 second-generation offspring, students begin to observe Mendel’s principles of segregation and the independent assortment of alleles, manifested through the 3:1 phenotypic ratio and 1:2:1 genotypic ratio. Students will obtain a practical comprehension of Mendelian genetics, learn to readily identify dominant and recessive traits, and absorb a durable and functional understanding of genetic terminology. This foundation, built through hands-on experimentation and a firsthand, participatory introduction to the scientific method, will provide students the tools they need to conquer more complicated tasks like constructing Punnett squares and, ultimately, acquiring the STEM skills they will need to compete in a knowledge-based economy.
Printed materials for this activity, background information, the software program, an optional accompanying PowerPoint presentation, and downloads are available at http://biotech.bio5.org/cooties. Other materials needed for the activity are trait factor sets (color cubes were purchased from http://www.eaieducation.com/), plastic cups, and computers. Setup for the activity is described below and is shown in detail on the website.
A teacher sets the scene, introducing the diverse habitat of the Sierra Madres and the fictional Cooties bugs that live there. According to the teacher, it has long been known that two different types of Cooties exist, each type having been considered a different species based on the differences in physical traits. Eastern Cooties live east of the Sierra Madres and have the physical traits of red body, wide ears, plain eyes, lips, and feet that look like boots, whereas Western Cooties live west of the Sierra Madres and have blue bodies, bow-shaped ears, lashes on eyes, tongues, and bare feet (as shown in Figure 1). Recently, researchers discovered that the two Cootie populations are, in fact, the same species, capable of sharing genes in nature (i.e., reproduction results in fertile offspring). This “new discovery” allows for a classroom discussion on speciation. (MS.LS-NSA)
Why are these Cooties, which are all the same species, so different? They have different body colors, ear shapes, eye characteristics, oral appendages, and feet. What adaptations have these populations acquired in response to their environments? What evidence might explain the variation in the species? What advantage have these adaptations given to each of the populations? Are these adaptations a result of natural selection, sexual selection, or random events such as genetic drift? Might there be an evolutionary tradeoff? Testable hypotheses can be presented and discussed in class. (4LCT-F, MS.LS-NSA)
Although the two Cootie populations are “true breeding” when bred with members of the same population, students will eventually inquire as to the outcome of a breeding between an Eastern Cootie and a Western Cootie. Initially, students predict and/or draw what the possible mating between these two different Cooties might yield, in terms of each of the five traits visible in offspring. (4.LCT)
Each Cootie has two trait factors for each trait. Because Cooties reproduce sexually, one trait factor per trait from each parent is passed, at random, to the offspring. The Cooties’ “trait factors” are represented as a colored cube and a corresponding letter, as shown in Figure 1. Traits and their trait factors are introduced individually to students. The trait factor set for the Eastern Cootie includes two of each colored cube – red, white, purple, lime green, and brown. Each trait’s trait factors are separated into cups (for example, the body color trait for the Eastern Cootie will constitute two red cubes in a cup). The trait factor set for the Western Cootie includes two of each colored cube – blue, black, yellow, orange, and green. If a Cootie is heterozygous, it will have one of each of the 10 colored cubes. Like alleles, cubes are given one-letter “names” that correspond to both the trait and the color of the cube for easy reference. The teacher introduces the Cooties software program, which will generate the results of mating two Cooties, correlated with the hands-on simulation of trait factors (colored cubes) passed on during mating. (MS.LS-GDRO)
During the mating of the true-breeding Eastern and Western Cooties, a first generation of new Cooties is produced. For the first mating, one trait factor (cube) from each of the parents (represented by five cups with trait factors for each of the five traits) is selected and recorded in the Cootie Program (Figure 2). The Cootie Program has been designed to take into account the laws of genetics and determine the physical characteristics of the offspring.
After the initial mating, students are asked to reflect on why all the Cootie offspring have exactly the same traits as the Eastern Cooties. What happened to the traits of the Western Cooties? Will these traits ever reappear within the population? Students can determine the relationship between “trait factors” and resultant “traits” by crossing the first-generation offspring with each other and evaluating the outcome. The first-generation offspring will carry one of each trait factor, and each trait factor will have a 50–50 chance of being passed to the second generation. In order to demonstrate this, groups of three are formed: one student randomly picks one trait factor at a time from the mother Cootie, another student randomly picks one trait factor at a time from the father Cootie, and a third student records all data into the Cooties Program. In this way, 40 second-generation Cooties per group are created.
After the second generation of Cooties is produced, students can explore the variation in the traits of the Cootie offspring simply by scrolling through the offspring shown on the screen. The data collected by the Cooties Program can be exported into an Excel file, where the total numbers of traits and “trait factors” can be tabulated, and the ratios and percentages of each trait and trait factor can be evaluated and compared to one another. If students chose the trait factors at random, the data from each group should be similar, with a 3:1 phenotypic ratio of dominant to recessive traits and an approximately 1:1:1:1 ratio of each of the trait factors, which ultimately will be simplified to a 1:2:1 homozygous dominant, heterozygous, and homozygous recessive genotypic ratio. Sample data are shown in Table 1.
|Trait .||Total # of .||Total # of .||Total # of .||Total # of .||Total # of .||Total # of .|
|Body color||RR||Rr||rR||rr||Red body||blue body|
|Eyes||PP||Pp||pP||pp||Plain eyes||lashes on eyes|
|Trait .||Total # of .||Total # of .||Total # of .||Total # of .||Total # of .||Total # of .|
|Body color||RR||Rr||rR||rr||Red body||blue body|
|Eyes||PP||Pp||pP||pp||Plain eyes||lashes on eyes|
Why don’t you get a ratio of exactly 30:10 every time? What would happen if you ran 400 crosses instead of 40? What would happen if you ran 4000 crosses? Group data can be compared and combined to show the overall patterns of genotypic ratios.
The resulting data about trait factors and expressed traits allow for an easy introduction to proper genetics terminology. Using this visual exercise, it is easy for students to see that one trait factor is “dominant” over the “recessive” and that a set of different trait factors are referred to as “heterozygous” and a pair of matching trait factors as “homozygous.” The ratios and notation of the “trait factors” can now be introduced and properly referred to as “alleles.” The introduction of proper terminology, coupled with the resultant data and ratios, should lead to an introduction and discussion of Punnett squares (Figure 3).
Math Integration Component
The integration of math and science is a very important thread throughout the Next Generation Science Standards, as depicted in A Framework for K–12 Science Education (National Research Council, 2012). Educational research has shown that learning from integrated subject matter promotes a less fragmented understanding and more effectively stimulates learning (Furner & Kumar, 2007).
Statistics and probability, which are themes in math standards for every grade level 6–8 (Common Core Mathematics Standards, http://www.corestandards.org/Math), can be discussed extensively through the introduction of this activity. Cootie Genetics can reinforce the concepts of probability and likelihood and promote the understanding of variation. In addition, students can graph their resultant genotype and phenotype data, as well as compiled class data, to understand the significance that sample size has for statistical data. Most classes will analyze each trait individually; however, studying the probability of two traits together (dihybrid cross) and extending these probability patterns to five traits allows for the introduction and application of complex mathematics.
Several teacher-formulated extensions could be incorporated into the original lesson plan. For example, introducing the class to the concepts of lethal or disease-causing alleles can raise questions about the genetic basis of human disease and also provide a context for discussing ethical standards. The implications of gene–environment interactions can also be discussed, depending on the traits introduced, as an environmental-health and human-impact extension. (MS.LS-GDRO, 3.EIO)
Teacher-generated data sets for linked genes could be provided to students. Using logic, patterns of association, bivariate analysis, frequency tables, and knowledge of heredity, students can come to understand how linked genes are distributed and how they function (8.SP.4. Math). In addition, sex-linked genes can be identified and their behavior explained.
Additional heritability extensions can be incorporated, such as codominance and incomplete dominance. The concepts of evolutionary tradeoffs, biological fitness, and the handicap principle can also be explored. What if eyelashes are correlated with poor eyesight, but with higher sexual selection? Mock data can be generated, followed by a mathematical analysis and graphing approach to demonstrate this phenomenon, just as the original scientists who worked on inheritance in various organisms once did.
In addition to covering requirements of the Life Science Standards, Cootie Genetics stands out as an effective way of reinforcing inquiry standards such as observation, generation of hypotheses, and making predictions based on evidence, probability, and/or modeling (National Research Council, 1996). Later introduction of genetics terminology enables students to interactively experience and understand the concepts before learning the associated vocabulary. Students will learn to associate “trait” with “phenotype,” to recognize “trait factors” as “alleles,” and to incorporate the remaining terms (genotype, dominant, recessive, homozygous, heterozygous, genes, and DNA) in a similar fashion, drawing upon their experiments. The advantage of introducing these terms at the end of the activity is readily apparent when working with students who are struggling to read, those learning English as a second language, and those with learning disabilities. Providing students with hands-on experiences and a preliminary conceptual foundation empowers them to understand the specialized scientific terminology, rather than simply memorizing it (Rupley & Slough, 2010). If students have already been introduced to genetics vocabulary, this activity has an alternative download, which includes genetics terminology.
Already, more than 200 teachers throughout Arizona have utilized Cootie Genetics in their heredity unit. Classes that have used Cootie Genetics have demonstrated superior student comprehension and obtained better test scores in subjects related to heredity and genetics, compared with classes in the same locations and with the same teachers prior to using Cootie Genetics. Teachers have often noted that applying this activity in the classroom allows students to immediately conjure up memories of the lesson and think through problems pertaining to genetics, even months later.
An independent analysis compared improvements in students’ understanding of genetics with and without Cootie Genetics. When evaluated by a genetics postlesson quiz, students who had conducted Cootie Genetics showed a 30% increase in their understanding of ratios and genotypic and phenotypic predictions, compared with the results from alternative teaching methods. Another analysis showed a 46% improvement in student comprehension of the effects of dominant and recessive alleles on phenotypes in classes taught using Cootie Genetics, compared with classes taught by the same teacher not using Cootie Genetics.
An evaluation of results from a small sample of students who took Arizona’s Instrument to Measure Standards exam indicated that students who had received the Cooties lesson scored 50% better on the science section of the exam than students who had not. In this teacher’s classes, Cootie Genetics led to overall higher student scores on the standardized science test.
It is important for all students to understand basic human genetics, because this is foundational to larger concepts of health and life sciences. Cootie Genetics allows for the practical and enduring instruction of concepts that are traditionally difficult for students to understand and retain. Ultimately, students will absorb a superior understanding of genetics, the laws of inheritance, and sexual reproduction by having conducted experiments similar to Mendel’s.
STEM job opportunities grew three times faster than non-STEM opportunities in the past decade, and over the next few years these opportunities are expected to almost double in comparison to non-STEM jobs (Rupley & Slough, 2010). Unfortunately, compared with their international peers, American students rank 25th in Math and 21st in Science (http://www.esa.doc.gov/Reports/stem-good-jobs-now-and-future). Without a full understanding and a newly applied emphasis on STEM concepts, including genetics, we will be doing our children a disservice by not adequately preparing them to compete for the fastest-growing and highest-paying jobs in a global market. Early exposure to, and confidence in, scientific principles has a direct correlation to career expectations and outcomes (Tai et al., 2006). Engaging, accessible, and entertaining lab activities such as Cootie Genetics are excellent tools to inspire early scientific exposure, curiosity, and understanding, and to imbue students with an enduring education that gives them the foundational tools to thrive in a knowledge-based, global economy.
We thank Qiyam Tung, UA Computer Science, for the original design of the Cootie Genetics Program; and Andrew Lenards (UA) and Calvin Dugger (Empire High School) for updates to the program. Thanks to all the teachers who have used the lesson, continue to use it with their classes, and offered suggestions for improvement. This work was funded in part by the Helios Education Foundation.