It's textbook that BP is genetic but there such a spectrum. My maternal grandmother was BP with psychosis because she was more interbred than my mom was who had BP. My dad's side of the family had no mental illness, but I still have BP1 however not to the degee as my grandmother or mom. My ex-husband has no mental illness on their side. If hypothetically, I had married a man with BP depending if both his parents had both or only on parent with BP, he could be on any part of the spectrum, meaning mild, moderate, or severe case.
I hope this makes some sense for family. Virginia Wolfe and Ernest Hemminway among others had generations of everything on the Bipolar Spectrum; including suicides.
Maureen