It's important to understand what it means to have a genetic predisposition. It simply means that in research conducted it was found, that people who's parents had clinical depression were more likely to suffer from it as well. More likely could mean simply that the percentage was a bit higher. It certainly doesn't mean, by any means, that the trait will pass on. There are other very important factors and it still isn't completely clear how all these factors interact.
I wouldn't worry to much about this issue. Better to invest time and resources in raising children in a happy way that will be healthful for them. physical and mental.