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I made the model chromosomes out of bendable hair rollers found at beauty supply stores. They come in a variety of widths and 9 5/8" lengths. I used 3/4" and 5/8" widths in two colors, gray and orange. They are easily cut with scissors for the foam and wire cutters for the wire core. I cut them into 5 7/8" and 3 3/4" lengths for the longer and shorter chromatids. I used permanent markers to add the stripes and for the alleles. Sticky back Velcro circles attached the sister chromatids together. I was also able to make it possible to demonstrate cross over by cutting off portions of the chromatids and reattaching them with Velcro circles. I made two sets of model chromosomes out of two packages of rollers. With 4 packages you could make 5 sets.