Although XX and XY are definitely the most common, differences in hormones and receptors in the body can lead to varying outward appearance (and inward feelings) about sex. For example, you can have XX chromosomes as well as congenital adrenal hyperplasia, where the body makes extra testosterone, leading to varying degrees of outward "male" development (if not managed with hormone medications). Similarly, you can have XY chromosomes, but have androgen insensitivity, where the body doesn't respon