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Im confused doesn’t the very fact that you have a XY or Y chromosome determine whether you’re male or female??
Are they not making physical genital differences relevant only to reinforce gender stereotypes?
What us your take on this?
Here’s my understanding: the body’s default is to be female, but there is a process in embryonic development which causes a male outcome instead. That process is kickstarted by a single gene, located on the Y chromosome, called SRY (sex-determining region Y), also known as testis determining factor (TDF). In the normal case, an XX becomes female because there is no SRY, whereas XY becomes male because Y contains SRY. However, if a Y chromosome’s SRY gene is damaged, the outcome will be an XY female (Swyer syndrome, aka XY gonadal dysgenesis); conversely, if the SRY gene is somehow translocated to another chromosome, you can end up with an XX male (de la Chapelle syndrome, aka XX male syndrome). Since SRY only kickstarts the process, and there are a number of subsequent steps, it is also possible for there to be SRY-positive XY females, where one of the genes responsible for one of the subsequent steps is damaged.
The Y chromosome is somewhat sparse, there’s not a huge amount there. Of course, there’s SRY. There’s a few genes which are slight variations of genes found elsewhere (e.g. the tooth enamel gene AMELY, where a very similar and functionally equivalent gene AMELX is found on the X chromosome), and also a bunch of genes involved in spermatogenesis (such as DAZ1, DAZ2, AZF1). This later point is part of why XX males are infertile, because lacking a Y chromosome they lack some essential spermatogenesis genes. (However, one should not think that genes required for spermatogenesis are only found on the Y chromosome - there are also a bunch of spermatogenesis genes on other chromosomes - in females, these genes are present, but they go unused.)
So, when people say XX=female and XY=male, that’s a simplification, albeit one which works 99.9% of the time. To say SRY-positive=male and SRY-negative=female is more accurate, although that is a simplification too. Since biological sex is a complex interaction of many factors, there is no one single factor which is by itself completely determinative. Of course, in the vast majority of cases, it is nonetheless clear to which biological sex a person belongs; but there are some very rare cases in which it is not very clear, and a person’s own self-identification is arguably a relevant factor then. (This later point is not a reference to transsexualism, since most transsexuals have no identifiable genetic abnormalities.)
(Also of interest - while humans, and a number of other animals, use the XY sex determination system, some other parts of the animal kingdom, such as birds and some fish and insects, use a different system instead - ZW. In XY, females have two identical chromosomes (XX) while males have two different (XY). In ZW, males have two identical chromosomes (ZZ), while females have two different (ZW). In XY, the gender of the offspring is determined by the sperm; by contrast, in ZW, the gender of the offspring is determined by the ovum. While in humans, female is the default, in many ZW animals, male is the default instead.)
Simon
