Why am I starting to act like my father?

I am a little perplexed by the fact that I am starting to act like my Dad, which at some points I am not so proud of. I catch myself acting like him in the sense at times I am pretty much saying to myself, "what am I doing, this seems like something my dad would do." Just a question, if anyone else is seeing something similar with themselves, please tell. I am just wondering if this is normal. Also, I really don't agree with my dad, I have never even looked at him as a father, I am closer to my step-dad.