X Chromosomes

Most of the time when I go to the library I am looking for a specific book. But once in a while I like to just peruse the shelves and see what catches my eye. I found a book all about the X chromosome in this way. It is called The X in Sex. I spent an hour or so reading it by the pool yesterday and it's pretty interesting stuff. As most of us know XX makes a girl and XY makes a boy. But the how of that is slightly more complicated...and it turns out its quite different (and pretty complicated)  for the two sexes. And they why of why we have two sexes (and not three or one) is also pretty interesting too.
Unlike the story of Adam and Eve, the human body is actually by default a woman. (It should have been Adam formed from Eve's rib and not the other way around.) That is, the body was designed to be a woman's, but with the substitution of the second X for Y it can be modified into a man's. The creation of a male is a more active process with genes coding for inhibiting certain processes and the alteration of the existing body plan, where creation of a female is more about just letting what is trying to happen, happen. Of course we are talking about mammals here.
One chapter of the book was on all the other forms of reproduction, some of which are truly bizarre. Some animals can change their sex half way through their lives, in some animals the ambient temperature surrounding the future offspring can determine it's sex, some animals have both sets of sex organs and can impregnate themselves! Aphids don't have males...just mothers and daughters, and in some marine species, males attach to a female body and loose all individuality (eyes, internal organs) and actually become a growth on the female, s a....sperm satchel. See the Angler fish below. (The only thing worse than being a sperm sack, is being a sperm sack attached to an female angler fish...ugggg gnarly.)
Anyway, I'm only half way through the book but it is really interesting. I'll write another post if I find any more noteworthy stuff!

Angler female and male