Like many other diseases, diabetes has a genetic component to it, but it is not directly heritable. Let me explain what I mean by this. First there are two general categories of diabetes known as type 1 and type 2. Type 1 is developed earlier in life and requires insulin use from day one. Type 2 may require insulin later in life, but can be managed initially with diet and oral medications. People with type 2 still make some natural insulin whereas people with type 1 do not. Type 2 diabetes has more of a genetic component to it. What this means is that people with a father and grandmother (such as yourself) with type 2 diabetes are at greater risk of developing it themselves, but there must be other factors as well. This means that maintaining a normal weight, eating healthy, and exercise can reduce your risk of developing type 2 diabetes.
Because you have a family history diabetes, you should probably get screened for it yearly at an earlier age than most other people. This way if you do begin to develop glucose intolerance (also known as pre-diabetes), then you can begin getting treated early.
I suggest that you schedule an appointment with your primary care physician
. He or she can provide you with more information on diabetes, specifically the type that runs in your family. You can get advice on how to prevent the development of diabetes, and any other complications to your health. Good luck.