Modeling Chromosomes: Building Paper Chromosomes to Help Understand Five Key Terms in Genetics

By Robertson, Carol | The Science Teacher, December 2016 | Go to article overview

Modeling Chromosomes: Building Paper Chromosomes to Help Understand Five Key Terms in Genetics


Robertson, Carol, The Science Teacher


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Learning about chromosomes is standard fare in biology classrooms today. However, students may find it difficult to understand the relationships among the genome, chromosomes, genes, a gene locus, and alleles. In this simple activity following the 5E approach (Bybee et al. 2006), students create paper models of chromosomes to learn how these terms are related and also to learn about the science and engineering practice of modeling.

This activity should come after students have been taught DNA structure, including complementary base pairs (Adenine-Thymine; Guanine-Cytosine). As background, I recommend completing the "I Am a Nucleotide" activity and having students make the chenille stem DNA models described in my earlier article (Roberston 2016).

Pre-class preparation

For a class of 24 students, cut 12 sheets of 8.5 x 11 inch paper of various colors in half vertically so you have strips that are 4.25 x 11 inches (Figure 1).

Engage

As students arrive in class, randomly give each student a 4.25 x 11 inch single strip of variously colored paper. I use blue, green, white, cherry, and yellow (Figure 1). Remind students of what they have learned of DNA structure, including the molecules making up the sides (deoxyribose sugar and phosphate groups) and steps of DNA (four types of nitrogenous bases: Adenine, Guanine, Thymine, Cytosine). If chenille stem models were made earlier in class (Robertson 2016), have students get out their models and review the structure of DNA.

Ask students to discuss with partners which part of the DNA has the information needed for cells to function. Answer: the base pairs. Explain to students that, although the sugar/phosphate sides of the DNA are important in the overall structure, we will only be showing the "steps" (base pairs) of DNA in this activity, since it is the order of the base pairs that conveys genetic information.

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Explore

Have each student hold their 4.25 x 11 inch paper in portrait orientation with the short sides at the top and bottom. Instruct each student to randomly write any sequence of the one-letter abbreviations for the four bases (A, T, G, and C) down the left edge of their paper. Students should write the letters as capitals and make them large enough so that 12-15 letters fit along the left edge (Figure 2). As students work, walk around the room to ensure they understand the instructions.

Next, have students write complementary bases along the right edge of their paper strip to correspond with the letters on the left edge. Be sure letters are written next to the long edges of the paper (Figure 3). Again, circulate to make sure students are doing this correctly and to give positive feedback. For clarity in these instructions, we will call this piece of paper with base pairs written on it a single strip.

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At this point, divide a larger class into two unequal teams (for example, teams of11 and 13). Then, ask students to group with other students from their own team who have the same color of single strips. Have students orient strips so the letters go the same direction, butt the short edges of their single strips together, and then tape them to make one longer strip of the same color within their small group (Figure 4). Connecting the pieces together works best if students use masking tape along the entire width of the 4.25 inch sides, sticking the tape on the side with no writing. We will call all the connected single strips of one color for each team a single-color strip.

Because you randomly handed out the 4.25 x 11 inch strips at the beginning of the class, the single-color strips in each team should vary in size ranging from a single piece (only one student in a team had that color paper) to several pieces together. The variety in the length of single-color strips within a team will be helpful later. …

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