Something doesn't add up right...is this 7 year old girl my sister?!?

Genetics is a funny thing. You should see some similarities between you and your "sister." Going off of that though, you may not see many things in common at all. Here's my family and we are all blood related. Me and my 2 brothers are all brown hair and brown eyes, my sister is blond hair and blue eyes. My brothers and my sister are all 5'10" or taller, I'm 5'3". What you need to look for are very subtle similarities. Does your "sister" look like your Aunts or Uncles? You can also look for a recessive trait that both your stepmom and your dad have. If you want any suggestions on those you can e-mail me kerinhanson@hotmail.com and I can look at pictures of your family and give you some ideas. Hope this helps!