Grandfather had colon cancer at 87, uncle had noncancerous polyps at 48. mother has no polyps. likely a colon cancer gene?

Likely Not: You have to have three or more family members with a confirmed diagnosis of colorectal cancer, one of whom should be a first degree (parent, child, sibling) relative.

Probably no: Not a terribly impressive cancer history but in my experience, both patients and docs could do a much better job when getting a thorough family history. If you are concerned, get all the family info you can (members with any and all cancers and even those without) and visit with your doc. I've told patients to do that and occasionally get a surprise.

Probably not: All cancer is a genetic disease in some way but if you mean did you inherit a gene that causes cancer, then this history, as bad as it may seem, is fairly common. To suspect a genetic predisposition to cancer of the colon, you would need more than one grandfather effected, actually several family members. But colon cancer is common and everyone, including you, needs screening in their 50's.