How the X Chromosome Controls our Lives

"Although many people are aware of the principles by which we are allocated our sex, I suspect few realize that this is a story rich in history, evolution, and philosophy that challenges our views of society."

p. 2.

"Male and female. He and she. Impregnator and gestator. The duality of the human race is such an inescapable part of our existence that throughout much of history few have ever wondered why it is so. Just as every person is irrevocably allocated a sex at birth, so is sexuality itself woven through the whole of human life."

pp. 5-6.

"At one point in the Generation of Animals, Aristotle states that 'the female is the opposite of the male.' as if the sexes are diametrically opposed counterparts that together make up the human species."

"Of course this was just a myth, but for the last two thousand years most Europeans have believed it."

p. 7.

"Our conclusion, when all the meaningless philosophical clutter is removed, is fascinating --men and women are made in fundamentally different ways. That are not two sides of the same coin.... they are more dissimilar than that. One is original and one is derived.

p. 33.

"It may be the Y chromosome that makes the obvious difference between men and women, but it is the X that makes them complementary rather than opposite. It is the X that eventually reunites them."

p. 170.

Warnings about genetics

So inheritance seemed to be a ubiquitous phenomenon, and yet nobody could explain it."

p.4.

"The cell divisions that made sperm and eggs seemed very different from the divisions that made all other cells. Instead of a single step cell division that takes place when other cells are made, the chromosomes go through a strictly choreographed sequence of two successive divisions, and during these divisions, they are in a state of constant interaction with each other."

Chromosomes, thus, had to be involved in inheritance.

p.5.

Making a difference:

"The human sex chromosomes are an odd couple....the X chromosome controls our lives in thousands of different ways."

p. 61.

"The X and Y chromosomes may be just a transient evolutionary whim, but they are central to our lives right now."

"The X determines whether we live at all. This is no longer just a matter of sex--it is a matter of survival.

p. 62.

"The DAX1 and SRY genes" are a testicle making combination of genes but not in a simple one to one way.

"DAX 1 is more than just a way of modulating the male-making activity of SRY; it is actually anti-male."

DAX 1 assures that "indifferent tissue" become ovaries

"other genes involved in sex determination are scattered over many different chromosomes--only the master switch has to be on the Y"

pp. 36-37.

inheritable disease | gender | sex | evolution | women

The hemophiliac curse

Duke of Kent, Edward Hanover, had a defective X Chromosome passed on to his daughter, Alexandrina Victoria, who in 1837 became Queen of England!

pp. 69-73.

Leopold, Victoria's son had hemophilia, inherited from her father's family. Her daughter, Alice's child Alexandra was to marry Czar Nicholas II and their child the Czarevich Alexander.

pp. 74-77.

Identical twin women may differ in ways men never do because of the women's possession of two X chromosomes.

pp. 145-147

sex specific chromosomes, the X chromosomes have to be inactivated in the female but activated to be passed on to male offspring.

pp. 138-142.

"So women's bodies truly are mixed--in a very real way that springs into relief when an X chromosome is damaged. Each woman is one creature and yet two intermingled as it were. Yet this spectacular but little mentioned wonder of nature may have still more to tell us about the prigin of the female of the species."

p. 151.

"One thing that is clear is that sexuality is far more complex than we ever realized. Geneticists' understanding of sexual differentiation has much advanced since" 1900s.

"Human beings are not simply male or female....'Intersexuality' is a fact of life, and not a particularly rare one either."

p. 167.

"later stages of the sex-determination process can go wrong, and all in all these bring the total up to about 1 percent of humanity who have a sexuality that differs from XX-female or XY-male....the human sexes are many and varied, and while two predominate,the others form a continuous spectrum that stretches between those two and beyond them."

qp. 167.

One percent of 6 billion is sixty million: 60,000,000 people worldwide.

"The importance of the X chromosome. It was discovered by chance, because although it looks much like any other chromosome, it seems somehow different, distant from the others. Unlike the brash male-making Y, it has great depth and complexity that make it a far more interesting controller of our destinies. It brings death and destruction to lone-X men and complexity and confusion to dual-X women."

pp. 167-168.

"Sex is essentially a cooperative venture."

"Why should the parental origin of their X chromosome make any difference.?" in the sociability of XO women?

"...the vestigial shriveled Y may play a minor role in actually making embryos turn into boys [via the presence of the SRY gene] ...but...the recurring theme of difference between men and women is the predominance of the X chromosome."

p. 171.

"particulate materiality"

inheritable disease | gender | sex | evolution | women

David Bainbridge, The X in Sex: How the X Chromosome Controls our Lives, (Cambridge: Harvard University Press, 2003).

Matt Ridley, The Agile Gene: How Nature Turns on Nurture, (New York: Harper Collins Press, 2003).

Evolution

Present-day sex chromosomes look very different from each other: The X chromosome comprises about 5 percent of the human genome, and contains about 2,000 genes, while the Y chromosome is quite small and contains only about 50 genes (Figure 1).

This striking difference in size and gene content between the sex chromosomes makes it hard to believe that they are actually ancient partners in a pair of chromosomes that originally were very similar. Once sex became determined by a genetic signal from the Y, the sex chromosomes largely stopped recombining in germ cells.

Degeneration of Y genes ensued, together with accumulation of genes that are advantageous to males on the Y chromosome, such as genes involved in testicular function and in male fertility. Similar genes appear to have accumulated on the X chromosome, so that the X chromosome also plays an important role in sperm production.

The X chromosome may also have a prominent role in brain function and intelligence. A strong argument in favor of this intriguing but still controversial theory is that mental disability is more common in males.

Human Genome research

genes | genetics | Evelyn Fox Keller | genetic resistance | human genome