Is depression hereditary?

I was just wondering because my mom has depression and I think my dad does too. I wouldn't know for sure about my dad because I only see him over Christmas and he ignores me when I'm there. He seems depressed to me, he tries to hide it though. Lately I have been depressed, probably for a year now. I started cutting... I think my mom also has bipolar disorder (she thinks so to). Is that hereditary? I need to know.