This was a small example to learn concepts, and it is much smaller than real genes. in a real gene, the exons average about 150 bases each and are almost always less than 400. introns can be highly variable in length but may be hundreds of bases. a small gene might have 4,500 bases and many exons and introns. remember that in this activity, each square was used to represent one base. one or two exons or introns might fill up a sheet of graph paper. how many pages would you need to represent a small gene of 4,500 bases? (figure out or count how many squares are on one sheet of graph paper. then figure out how many sheets would have 4,500 squares.)