Children inherit the 5-HTT gene from their parents, so having a history of depression in the family can increase your risk of developing it. In other words, you have a ‘genetic predisposition’ for depression. On the other hand, many people who have a family history of depression never develop the condition.
It depends upon the type of depression. Bipolar disorder (previously called manic Depression) is highly heritable for depression. Interestingly, the most common psychiatric diagnosis in offspring of parents with bipolar disorder is major depressive disorder - not bipolar disorder