Hi Mam. Diabetes is caused by many factors coming together. This includes genetic causes( inheritance from parents) and lifestyle changes. Since his dad is diabetic, there are more chances that he may get diabetes but if he leads a healthy lifestyle he may not get it. Even there is no diabetes in the parents, some  develop diabetes if their lifestyle is not good. So good habits from childhood like proper diet and exercise, avoiding smoking, avoiding  alcohol etc are extremely important to maintain good health and avoid diseases like diabetes, cancer, high blood pressure etc. Other important cause for many diseases is environmental pollution (air, water, earth and noise) which has to be minimized by collective efforts.