How to mutate a seed at home?

For my gr.12 biology class we're doing a lab on seeds for our genetics unit. Each student is to pick a factor which we would test on a seedling before it is planted to affect its genetic structure which we are to examine later after we plant it (weirdness in the chromosomes of the plants stem cells). I'm having some difficulty picking a factor though :s. I know that the type of soil,light, water, and temperature affect a plants growth, but does it change it genetically as a seed? Any suggestions as to what i can do to the seed? Please note that I do not have access to things like advanced chemicals or nuclear radiation, something practical please!