Are ulcerative colitis and crohn's disease hereditary?

Somewhat: There are numerous families where there are children and /or grandchildren, cousins, etc. With these diseases. If both parents have ibd, the incidence is around 50% in the kids. Otherwise about 20% of patients will have a first degree relative with ibd. So you do the math! it isn't exactly hereditary, but there a familial incedence. By the way, the kids of colitis patients often have crohn's.

Yes: Although many patients can be diagnosed with crohn's disease or ulcerative colitis without a family history, up to 10% of patients will have a mother or father with the disease.

Not really: There is a genetic component and risks for ibd are higher in those witha family history. However there are a multitude of other contributing factors.