Quote:Can someone get me more info about what this "y" turning around thing is? I hope they aren't talking about yy syndrome..
During meiosis (the process by which normal cells turn into sperm and eggs), "matching" (or homologous) chromosomes line up together and "cross over" -- that is, some genetic material is exchanged between the two chromosomes, which then migrate to opposite ends of the cell before the cell divides. This helps ensure that the chromosomes in the daughter cells are not the same as those in the parent cell, and helps increase genetic diversity in a population. This is recombination. Apparently this happens very little or not at all with the Y chromosome, which may lead to ongoing and eventual diminishment over many generations as any genetic material lost from the Y chromosome may not be replaced, as it were, during meiosis. Probably the Y chromosome was complete way back there in evolutionary time and was accidentally reduced somehow, but I'm not up on my genetics, so I don't know when or in what. Given the diversity of sex deterination mechanisms in the insects, I expect it occurred prior to the evolution of the chordates (loosely translated, the vertebrates), but, again, I'm just speculating and possibly misremembering some things here. Since the Y chromosome was conserved, though, I suspect it must have conferred some advantage or other.
Incidentally, female mammals only use one of their sex chromosomes, anyway. Early in development, one of the X chromosomes becomes dormant and lodges itself on the inside of the nuclear envelope of the cell -- it's called a Barr body. This happens some time after the first cleavage of the zygote, though, and it happens randomly, so as an organism the female does have the advantage of expressing genes from both chromosomes.
Does that help at all?