Some of you were asking for further info about the genetics of sex, so here's what I've got.
Here's the Amazon link to “Between XX and XY: Intersexuality and the Myth of Two Sexes”. There are some points were I think the book could do a better job of staying away from gender assumptions, but overall it's a great layperson's intro to the uber-complexities of the physiology of what we call “sex”. I got it from my local library, so if your library doesn't have it they'll be able to get it via Interlibrary Loan.
If you really want to dig your teeth into the real research (hi Jen!) here are a couple of citations. There is also a bibliography in the back of the above-referenced book for further research.
Clarnette, T., Sugita, Y., & Hutson, J. (1997). Genital anomalies in human and animal models reveal the mechanisms and hormones governing testicular descent. British
Journal of Urology, 79, 99-112. Gravholt, C., Juul, S., Naera, R., & Hansen, J. (1998). Morbidity in Turner syndrome. Journal of Clinical Epidemiology, 51, 147-158.
Kruse, R., Guttenbach, M., Schartmann, B., Schubert, R., van der Ven, H., Schmid, M., & Propping, P. (1998). Genetic counseling in a patient with XXY/XXXY/XY mosaic Klinfelterâ€™s syndrome: Estimates of sex chromosome aberrations in sperm before intracytoplasmic sperm injection. Fertility and Sterility, 69, 482-485.
Book: Levitan, M. & Montagu, A. (1977). A textbook of human genetics (2nd ed). New York: Oxford University Press. Sarah, if you have any more, please share them. Or anyone else too.