Woman: An Intimate Geography by Natalie Angier Read Free Book Online Page A

thousands of brilliantly lit buildings suddenly blinked off. Click! cries a liver cell. There goes mother love! But then a brain cell makes up its mind, and the maternal chromosome is kept alive while the father X is nullified. Not every gene is shut off on the so-called inactivated X; a few stay lit, to match the handful of genes found on the male's dwarf of a Y chromosome. Nevertheless, thousands of genes are dispensed with in a given cell, and they are either thousands from the mother or thousands from the father.
So we can understand why the hirsute girls demonstrated such outstanding discrepancies in appearance. The gene behind congenital hypertrichosis, the atavism that once helped lend us a mammalian mantle, is located on the X chromosome. In most of us, the gene doesn't operate. The shaggy look does not suit human aesthetics, it doesn't do much to attract a mate, and so the gene has fallen fallow. But in the family with hypertrichosis, the gene has risen from its coma. It works. It makes a kind of fur. Each of the girls has inherited one copy of the fully awakened gene, Esmeralda and Rosa from their mother, niece Maria from her father. And each child is a mosaic of X chromosomes with the trait and X chromosomes without. Esmeralda's face is thus largely the face of her father, he of the unaffected X. Just by chance, the vast majority of the follicle cells on her cheeks, forehead, nose, and chin switched off the maternal X chromosome, allowing the unaffected paternal chromosome to dominate her appearance and thus keep the mark of the werewolf at bay. Her sister's face took nearly the opposite path, the cells switching off the paternal chromosome and putting the woolly maternal X to work. Maria ended up with six of one, half a dozen of the other. All was chance, all was a crapshoot. The switching

     

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pattern of the chromosomes could as easily have gone the other way for the sisters; and indeed, if they themselves have daughters, the child of the merry popular one could prove to have cheeks that feel to the touch like the face of a cat.
The world may not make it out so easily, but we are all of us gals strange little quilts, patches of father-tone in some of our tissues, shades of mother in the others. We are more motley by far than our brothers. A son, in fact, may rightfully be thought of as a mama's boy: he has her X chromosome alive in every cell of his body. He has no choice it's the only X he's got, and every cell needs it. Thus he has more of his mother's genes operating in his body than he does of his father's, thousands more. Yes, the Y chromosome is there, and that is solely a father-to-son transaction; but remember that the Y is genetically impoverished compared to the X. If you do the calculations, your brother works out to be about 6 percent more related to your mother than to your father, and he is 3 percent more related to your mother than you are, because half your cells, on average, have the mother chromosome turned off, while all of his remain turned on. These are not inconsequential figures. In a way, I'm sorry to mention them. They disrupt the image of the matriline, of our female connectedness to the ancestral parade of mother, grandmother, great-grandmother, the blessed founding matriarch. (On an interesting side note, male identical twins are more identical than female twins, again as a result of X inactivation. Male twins share the totality of their maternal X chromosomes, as well as having all the other chromosomes in common, but female twins have a diverging patchwork of maternal and paternal X chromosomes operating in different parts of their bodies.)
Men, perhaps, will be hardly more delighted at the thought of their maternal vinculum. Don't men want so badly to individuate , to pull away from the omnipotent female who dominated their world for the first fragile years of their lives? And then to find out that she is more a part of them than they thought! I know my father would