You can be destined to become a doctor because of an inner passion. If your parents and siblings, and aunts and uncles are all doctors; being a doctor may be your destiny because of the huge influence of your family. Your destiny can be the result of fate, or luck, or inner passion, or hard work, bad choices, or some generic spiritual ordination, or anything else.
Predestination is a word more reserved for the idea that your destiny was decided by God before you were born.
Dominate means (to rule over or the most noticable) ... Example: She was the most dominant girl in class mainly because she was bossy but also because she was very pretty.)
Predominant means to be the strongest force or have the most numbers. Example: In China, girls predominate the boys in most classrooms because there are most girls in China than boys. However, the boys predominate girls in social order since boys are still valued more than girls.