As for Type 2’s, there is a very strong genetic component, but also some kind of trigger that activates the diabetes. They have identified at least 13 genes associated with Type 2 (and there are probably a lot more). And who knows what the pollutants and toxins we are exposed to are doing in our bodies – when a Type 2 succeeds in losing weight, it just releases more (probably) harmful chemicals into the body.
Type 2 genes do NOT lead to Type 1, because as others have said, they are really 2 different diseases, although they overlap in many areas, such as auto-immunity, and insulin resistance. But there nothing about having Type 1 that will protect you from developing metabolic syndrome, and the insulin resistance characteristic of Type 2. So you can actually have both at once. I personally know one person who does.
This is such a complicated subject, and the scientists themselves know so little about it, why should we think we know any better???