How can we use our knowledge of genetics to predict or control particular characteristics?

I am certainly no expert in this area, but I think it is
clear that our ever-increasing knowledge concerning genetics is already being used to
make predictions and, to a limited extent, to control certain characteristics. In
particular, I am thinking of the specific example of the way that scientists are now
able to identify a breast cancer gene, which if you have it means you are much more
likely to contract the disease at some point in your life. I believe similar discoveries
have been made in terms of a gene indicating Downs Syndrome. Certainly, this is
something that we can only expect to increase as our knowledge of genetics and in
particular our identification of particular genes resulting in conditions or syndromes
grows. This of course does bring with it massive ethical and moral issues, which must
not be ignored.