SnapAttack - I put my hands up and say I know very very little about this area and would like to know more and understand it better
Well then quit with the 'I am a biology teacher' appeals to authority.
First of all, in a sexual species, you can have females be XX and males be X (insects)
But we are not insects ...
you can have females be ZW and males be ZZ (birds)
... neither are we birds ...
you can have females be females because they developed in a warm environment and males be males because they developed in a cool environment (reptiles)
... or reptiles ...
you can have females be females because they lost a penis sword fighting contest (some flatworms)
... or fucking flatforms ...
you can have males be males because they were born female, but changed sexes because the only male in their group died (parrotfish and clownfish)
... or fish FFS!
you can have males look and act like females because they are trying to get close enough to actual females to mate with them (cuttlefish, bluegills, others)
Still not fish.
or you can be one of thousands of sexes (slime mold, some mushrooms.)
Now you're just being silly.
Oh, did you mean humans?
YES! (but mammals as a group will do.)
Oh ok then. You can be male because you were born female, but you have 5-alphareductase deficiency and so you grew a penis at age 12.
A rare disorder of sexual development (Intersex condition) Most affected individuals are unable to have biological children without assisted reproduction.
You can be female because you have an X and a Y chromosome but you are insensitive to androgens, and so you have a female body.
A rather more common disorder of sexual development (Intersex condition). People with AIS are not fertile.
You can be female because you have an X and a Y chromosome but your Y is missing the SRY gene, and so you have a female body.
Swyer syndrome is another disorder of sexual development (Intersex condition). Individuals with this condition are infertile. They have undeveloped gonads which are usually removed because they have a tendency to become cancerous. Swyer syndrome may also occur along with health conditions such as nerve problems (neuropathy) or as part of a syndrome such as campomelic dysplasia, which causes severe skeletal abnormalities.
You can be male because you have two X chromosomes, but one of your X's HAS an SRY gene, and so you have a male body.
Male XX syndrome is a disorder of sexual development (Intersex condition). At puberty, most affected individuals require treatment with the male sex hormone testosterone to induce development of male secondary sex characteristics such as facial hair and deepening of the voice (masculinization). Hormone treatment can also help prevent breast enlargement (gynecomastia). Adults with this disorder are usually shorter than average for males and are unable to have children (infertile).
You can be male because you have two X chromosomes- but also a Y
Klinefelter syndrome is a disorder of sexual development (Intersex condition). The primary feature is infertility. Children with Klinefelter syndrome may have learning disabilities and delayed speech and language development.
You can be female because you have only one X chromosome at all
Turner syndrome is a disorder of sexual development (Intersex condition). It causes infertility and a whole host of physical complications. Girls and women with Turner syndrome will need to have regular health checks of their heart, kidneys and reproductive system throughout their lives ... Life expectancy is slightly reduced, but it can be improved with regular health checks to identify and treat potential problems at an early stage.
And you can be male because you have two X chromosomes, but your heart and brain are male. And vice - effing - versa.
This is not a disorder of sexual development, it is gender bullshit. Intersex people have requested that they are left out of discussions around trans:
Intersexuality is not the same as a transsexuality (gender dysphoria) and is not a transgender state. Neither of the latter terms is one that we recognise as belonging in any general discussion of intersex. We are not happy with the recent tendency of some trans groups/people to promote transgender as an umbrella term to encompass, for example, transsexuality, transvestitism and intersex. We object to other organisations/individuals putting us in categories without consulting us, especially categories that imply that interexed people, of necessity, have gender identity issues.