Is it weird I look like no one in my family?

[chaotichazard]

My mother has natural blond hair, my father has natural red hair. I have black hair. No one in my family has black hair. All of my family that I know has a birthmark on either their right leg or on their ankle, I don't. I mean people tell me that I look adopted all the time. I am the 2nd tallest person that I know in my family(tallest being my grandfather). I also have curly hair, while everyone but my aunt has straight hair.

So, is it possible I am adopted or is it normal for some people to look nothing like their family?