More on chromosomes -- now with evolution & cars

Of course the good Professor Myers over at Pharyngula read the whole Nature article about the sequencing of the human X chromosome, and he provides a beautiful and really pretty accessible accounting of its evolutionary story. Way more interesting than the BBC article I comment on below. Please do check it out here if you're interested in that kind of thing. For one thing, it sorta sets me straight on the role of the X chromosome in the whole sex differences thing. He says, "All human beings are adjusted to having just one fully functional X chromosome, no matter whether you are male or female," and explains further:

"Another misconception that I often see is the idea that the X chromosome is the 'female' chromosome, while Y is 'male'. Avoid that bias. We males also have an X chromosome, and are as dependent on it as are females, and maybe more. The Y chromosome bears almost none of the genes that will be selectively activated in males as they develop. Most of those genes are scattered throughout the genome and are present in both sexes (yes, ladies, you have most of the ingredients to build testicles, just as we gentlemen also contain the complete secret recipe for ovaries in our cells). In fact, the X chromosome is a favored place to stash male-specific genes."

And for another thing, his post explains very lucidly the concept of recombination with a very efficient analogy:

"Recombination is a kind of repair mechanism; not a clever one, but one that can have long term effects. Imagine a very stupid mechanic who maintains two cars by constantly swapping pieces from one to another. If one has a broken carburetor, at least one car will function. If one has a broken carburetor and the other has a broken alternator, every once in a while in his manic swapping, one of the cars will end up with both functioning components, and the other both broken ones: that means there will be at least one car he can send off the lot. Note that this is not a viable business model for a human garage, but it works well enough in a ruthless sort of way for biology. While it produces junk cars as well as good ones, most of the junkers blow up as they're leaving the lot, so no one survives to complain, and all anyone sees actually traveling down the road are the lucky products of random exchanges, and it's only those lucky drivers who go on to make more cars."

This also explains why my father always had two of the same cars -- the two 1963 Ford Falcons (a black station wagon and a white sedan), the two late-sixties Chevy Novas (ditto, but green and blue, respectively), and the the two early seventies Cadillacs (a gold Coupe de Ville and a silver Fleetwood) -- and I seem to remember that if something went wrong with one, the other would suddenly be out of action for a while. He was recombinating them. Or whatever.