A student makes a DNA model from pipe cleaners of the following quantity and color: 80 red, 80 blue, and 80 white. She connects red to blue and continues until she has completed an 80 pipe-cleaner strand, and repeats the process to make a second strand. She then randomly attaches a green or white pipe cleaner to every blue pipe cleaner in the strand. She repeats the process on the other blue strand but places the green and white in the exact opposite pattern she used on the first strand. In this model, the green and white pipe cleaners best represent the