Sex and gender

Hi all - I'm still here! I've been away on holiday for a week, and I guess I don't have as much to say as I used to .....surprising, I know.
I've been catching up on my Sociology subject this week (as I discovered I have an online exam to do and hadn't done much reading at all for this subject!). A lot of the subject matter has been about our idea of 'self' and our identity in society. Today the reading's been about sexual identity and gender identity - and are they the same thing or different?
It's been interesting reading, and studying this stuff has certainly helped me to be a bit more broad-minded which I think was actually necessary. The authors of the text book (of course) have the view that gender and sex are very different. It brings about a lot of interesting ponderings I think.
I have typically defined sex by the biological definition - which genitalia do you have? (not to put too fine a point to it!) But now we have in society a new term called gender which is more along the lines of which sex do you identify with for yourself? A person can have male genitalia but identify as a woman (or vice versa). So what makes us male and female? According to my text book we are all conceived female and then at some point in-utero the embryo with the XY configuration gets a testosterone wash and becomes male. But there are lots of variations genetically too. 'Men' can have XXY chromosomes, usually resulting in a very effeminate male. Apparently (and I didn't know this til I read it in the book) in the late 80's the women who were performing well at Olympic field events were tested genetically. They were found to have male chromosomes!
On a personal level this issue of gender identity has been something I've given more thought to since my marriage breakdown. Whilst D is 'male' and presents as 'male/masculine' he obviously has something going on somewhere in his genetics or socialised identity..... The underlying issue is are people born male and female, are they made male and female by society or is it some kind of combination? And what about those who have (for example) male genitalia and identify as male until puberty (or some other time) then feel they actually should have been born a woman?
It's all very interesting, and one thing I am becoming more certain of - I (and we) can't label situations or other people's experiences based on our own (often limited) experiences. The world is made up of a very comlex mix of people. None of us completely fit any mold/stereotype.

"For you created my inmost being; you knit me together in my mother's womb. I praise you because I am fearfully and wonderfully made." Psalm 139:13-14