Chromosomes, alleles, chromatids, genotype, phenotype, mitosis, meiosis, fertilization--this vocabulary can be overwhelming, confusing, and difficult for students to tie together. However, these terms are commonplace in the high school biology classroom; they are the basis for understanding both DNA and heredity. Students must understand these topics not only for state testing but for everyday applications, as well. But how do we teach them so that students truly understand them?
As high school biology teachers with limited budgets, we are always on the lookout for inexpensive ways to teach DNA and heredity. We have tried pipe cleaners, flip books, coloring worksheets, and online lessons--but one of our best discoveries was made in the swimming pool. Brightly colored pool "noodles" make great chromosome models, and since they are seasonal in most places, they go on sale at the end of summer. We paid less than $1 per noodle!
In this article, we explain how we use noodles to help students gain a greater appreciation of the interdependence of DNA and inherited traits.
Noodles as models
Many of the lessons and demonstrations we attempt in our classrooms use nonlinguistic representation and cooperative learning. We find that student comprehension increases dramatically when mental imagery and kinesthetic learning are incorporated into classroom activities. Working cooperatively in groups enhances student understanding, and completing this kind of activity encourages interactions between students and teachers--increasing both knowledge and recall ability (Marzano, Pickering, and Pollock 2001).
For this activity, we buy noodles in two different colors and cut, modify, and tape them to make noodle chromosomes, or what we call chromonoodles. Students love them because they are fun, colorful, and big enough for all to see. We love them because they are easy to make, inexpensive, and can be used repeatedly to introduce, demonstrate, reinforce, and make connections between genetic concepts.
Making chromonoodles is easy and requires only a few inexpensive supplies: six pool noodles in two different colors to represent the sexes (we use three blue and three green), permanent markers, and several colors of tape in different widths.
The number of chromosomes symbolized can vary, depending on the availability of noodles and your ability to store them. Representing the entire human karyotype--23 chromosome pairs--is too bulky and cumbersome, so we start with 6. Cut the noodles into six groups of four chromosomes. Within each group, there are two chromonoodles of each color (e.g., in our case, two blue and two green) and all chromonoodles are the same length (Figure 1A). Vary the length of the chromonoodles from group to group--except for the X and Y pair, which should be cut so that the X chromonoodle is longer (Figure 1B). This allows the set to be used for the cell cycle, mitosis, and meiosis.
Next, using the colored tape, make a pattern on the four same-size chromatids. The tape represents the banding pattern found on an actual karyotype of stained chromosomes. You can use different colors, widths, or types of tape--just make sure that the four same-size chromatids also have the same pattern. Repeat in varying patterns for each chromonoodle (Figure 3, p. 36). (Note: The bands represent regions of DNA that stain differently. Depending on the section of the chromosome, there may be hundreds or very few genes in each band, so students should not misinterpret the bands as representing a single gene.)
Use a marker to write letters on the bands, representing alleles on the different homologous chromosomes. Make sure that the two chromatids that are the same size and color also have identical letters--including identical capitalization, since they represent identical sister chromatids; this demonstrates the end of the S phase during the cell cycle. …