Colored, banded yarn. For example, the yarn may change from red to white to green or some other combination of colors. Pass out pieces of the yarn to students. Use the yarn as an example of the linearity of DNA and the distinct segments of the DNA sequence that are genes, i.e. the different colors. Let the red represent one gene, the green another, and so on.
Students can tie knots in the yarn to represent mutations.
The yarn provides a simple illustration of DNA and genes that is both visual and kinesthetic.