Genetics. Since your dad is o-, the only blood type he can give you is o-. Your mom, being b+, can still pass on to you an o- blood type depending on the blood types of her parents. Here is a pretty good tutorial on the genetics of ABO and rh blood types. Http://www. Biology. Arizona. Edu/human_bio/problem_sets/blood_types/intro. Html.
Yes. Yes, it is possible for you to be o-.