You are living with my agony.  I, too, wonder what the chances are.  I can tell you that I am the daughter of a "manic-depressive" mother.  I can also tell you that, in my opinion, I had 2 grandmothers (both sides) who exhibited symptoms...but were never diagnosed.  Is it heredity or that I learned it by example?  Who knows?  I know that I am one of 4 girls and that ALL of us have been in therapy at some point.  I am the only one with a label.  The other 3 work in the medical community and their docs write their scripts w/out labeling.  Are they?  If they are, you'll never get them to admit it.  My kids....oh my.  I live in fear everyday.  I do know that I will hold their hands and be there for them if they are ever diagnosed and even if they are not.  Bipolar is not a terrible thing.  The ignorance of our society has made it a terrible thing.  If you look at the list of Bipolar people, you'll find you're in pretty good company.  That is until your local people find out...then, you have to find friends who do understand that you are no different than a diabetic....your chemicals are off and you have to take your meds.  That's all.  Good Luck!