Have you heard about epigenome? Well they (scientist) are not saying that there is something that sits on the surface of genes called epigenome. This epigenome, depending on the environment triggers the genes to act a certain way. And the effect can take place up to three generations back. So for example, if a grandfather was fed well as a child, the grandchild has a better chance of being diabetic.

PBS (I believe NOVA) just did a whole study on this. I was pretty fascinating.