Many people often use the terms "sex " and "gender" interchangeably, however, some people now assign them two different meanings. They use the term "sex" to refer to the biological assignment of an individual, which is often based on scientific knowledge. This biological determination is often made at birth. Doctors often assign sex by looking at pre-natal images or directly inspecting genitalia at birth. This determination is still based on our beliefs on gender and sex being the same. The problem lies in what happens when an individual falls outside of the typical categories of "male" or "female". Some medical professionals have turned to the Karyotype method to look at the sex chromosomes to determine biological sex. "Gender", on the other hand, is considered by some to be more of a psychological factor. To them, gender is determined by our expressions, and behaviors rather than scientific knowledge. 