To What Extent is Gender Purely Biological?

I believe that the presence of either xx chromosomes or xy chromosomes creates a purely biological distinction between female and male. The farther one moves from the chromosomal level, the murkier gender issues become.

We rely heavily on our own social and psychological experiences in interpreting the physical traits that biochemistry has generated and the behaviors that biochemistry and socialization have created.

In assessing ourselves, we encounter our inner selves first and tend to look to others for confirmation of our self-beliefs. As individuals evaluating others, we encounter their outward appearance first and rely upon it to assess gender, often know nothing of another's inner self. The process is interesting, perhaps distorting perception as funhouse mirrors do.