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Excerpted, with minor changes, from Eves Rib - Searching for the Biological Roots of Sex Differences by Robert Peel (Crown Publishers, New York, 1994, ISBN 0-517-59298-3).
ln l985, when she travelled to Kobe, Japan, to compete in the World University Games, Spanish hurdler Maria Patino [María José Martínez Patiño] got the shock of her life. Like other female competitors there, she had to take a sex test to prove she was not a man in disguise, but she wasn't worried. She had passed a similar checkup once before, and anyway, she had no doubts that she was a woman. That faith was about to be tested. Although most people outside the athletic world never hear about sex testing, world-class female athletes know it well. It began at the 1966 European Track and Field Championships in Budapest in response to consistent rumors that some of the best women athletes from the Soviet Union and Eastern Europe were actually men. That year the women at the meet had to parade naked in front of a panel of gynecologists. Although none were disqualified, several of the Communist competitors - including Tamara and Inira Press, who between them had won five gold medals and set twenty-six world records from 1959 to 1965 - failed to show up for the test. This convinced people that the sex test was a good idea. Two years later, to screen women athletes at the Summer Games in Mexico City, the International Olympic Committee settled on a more dignified method than the "nude parade" - a newly developed procedure called the buccal smear. A lab technician would scrape a few skin cells from the inside of a woman's cheek, then stain the tissue sample and examine it under a high-powered microscope. If the cells had two X chromosomes - the mark of a genetic female - then the technician would see a dark spot inside the cell's nucleus called a Barr body. If only one X was present, as is the case with genetic males, then no dark spot appeared.
It was this test that Maria Patino took in 1985 to prove she had no unfair advantage over the other women hurdlers. When her results came back, however, there were no Barr bodies in her cells - genetically she was a male, the test said. Meet officials told her she would not be allowed to compete, and advised her to fake an injury and leave. But convinced that she was just as female as the other competitors, she continued training and entered a meet in Spain several months later. Ignoring a warning not to compete from the president of the Spanish athletic federation, she won her event, but the following week she was kicked off the Spanish national team, stripped of her titles and barred from competition. Two and a half years later she was reinstated by the International Amateur Althetics Federation.
Is Maria Patino the woman she appears to be or the man that the buccal smear says she is? She is not a transsexual - that is, someone who has undergone surgery to change from one sex to another. She has been a female all her life. But neither was there a mistake with the buccal smear - she does not have two X chromosomes. So what is she (or he)? The answer takes us to the heart of what makes a male or female. Sex seemed so simple back in school biology class, when the teacher explained that it all depends on the twenty-third pair of chromosomes, the sex chromosomes. A woman has a matched set of two X chromosomes, which appear long and elegant when seen under a high-powered microscope. A man has only a single X escorted by a short, squat Y chromosome. But for Maria Patino the simple answer just won't do. She has one X and one Y chromosome, not two X's, yet to all appearances she is a female. To understand her sex, we must go past the chromosomes to see how a body develops in the womb.
A human embryo is neither male nor female for the first seven weeks after conception. It is essentially neuter, and it is impossible to tell an XX fetus from an XY fetus without peering deep into the individual cells and examining the sex chromosomes themselves. At seven weeks the fetus has an embryonic reproductive system consisting of a pair of gonads, which can grow into either ovaries or testes, plus a mass of tissue called the genital ridge, which can develop into either a clitoris and labia or a penis and scrotum. There are also two primordial systems of ducts, one female and one male, The female ducts, called Mullerian ducts, grow into the uterus, fallopian tubes and part of the vagina if the fetus heads down a female path, while the male, or Wolffian, ducts are the precursors of the usual male plumbing - the seminal vesicles, vas deferens and epididymis.
During the eighth week the fetus chooses between two paths: masculine or feminine. If the fetus is genetically male - if it has a Y chromosome - then a "master switch" on the Y chromosome clicks on at this time. This switch, which is a single gene called the testes-determining factor, triggers a whole series of events that will point the fetus in a male direction and culminate in a baby boy - if everything goes as planned. The flipping of this switch is the key step. The testis-determining factor signals the embryonic gonads to form into testes, which then begin to produce male hormones, and the hormones take it from there. The major hormone produced by the testes is testosterone, which stimulates the Wolffian ducts to start developing into the male duct system. At the same time, some of the testosterone is converted by the body into a second male hormone, dihydrotestosterone, which prompts the genital ridge to begin forming into male genitals. The testes also produce a substance called Mullerian inhibiting factor, which causes the (feminine) Mullerian ducts to atrophy and eventually be absorbed by the body.
A female fetus, on the other hand, doesn't have a Y chromosome and so the master switch is never turned on. Nothing happens in the eighth week. Instead the fetus continues to grow and develop, and in the thirteenth week the gonads start to transform into ovaries. With no testes to churn out large amounts of male hormones, the rest of the sexual system, internal and external, develops in a female direction. The genital ridge evolves into the clitoris and labia, and the Mullerian ducts mature into the uterus, fallopian tubes and upper one-third of the vagina. The Wolffian ducts shrivel up. In other words, the "default" body plan is female, and a fetus will go down this path unless diverted. It is as if the God of the Bible, in a departure from the usual story, actually made Eve first, then took one of her ribs, added some testosterone and other male hormones, and presto: Adam.
So sex is much more a matter of hormones than of chromosomes. Indeed, the small Y chromosome, the root of all maleness, seems to do little besides turn on the "master male switch" to start the flow of hormones. The Y holds relatively few genes, and most of them are duplicates of genes that lie on the X chromosome - as far as researchers know, only a handful of genes are unique to the Y chromosome. These include the testis-determining factor, a gene involved with male fertility and making sperm, and a third called the H-Y antigen gene, which, as far as researchers can tell, has nothing to do with sexual differentiation. In short, the Y chromosome is little more than an abbreviated version of the X with the gene for the male switch tacked on. In practical terms, this arrangement means that it is the hormone environment of the womb, not the chromosomes, that directly determines the sex of the fetus.
In humans, approximately one of every twenty thousand genetic males has a defect in his "androgen receptors" - the large molecules that act as middlemen between male hormones (androgens) and the various tissues in the body that these hormones act on. And in essence, this is what happened to Maria Patino. When such receptors are working right, they grab hold of molecules of male hormones and then bind to the DNA in the cells, triggering a variety of biochemical events that eventually lead to such things as the growth of the penis and scrotum. The hormones cannot turn on these events by themselves - they need the receptors, and if the receptors are defective, the body will not respond to testosterone and the other male hormones. In such cases of "androgen insensitivity," the XY fetus will develop testes around the eighth week of gestation, right on schedule, and soon afterward the testes start producing testosterone and sending it out into the body. But as far as the rest of the body is concerned, the testosterone isnt there. Because the receptors are faulty, the body cannot detect any male hormones, so the genetically male fetus never hears its "male call" and instead heads down a mostly female track. The testes still do produce Mullerian inhibiting factor, however, so the Mullerian ducts atrophy and the fetus never develops a uterus, fallopian tubes or the upper part of the vagina.
At birth, the child looks like a girl. The only sign that something is different is the presence of the testes, either in the labia or in the lower part of the groin, but doctors will miss those without a close examination. At puberty, the girl develops breasts and a woman's body. Although she has no ovaries to make female hormones, her body transforms some of the testosterone and androstenedione produced by the testes into the female hormone estradiol, and there is enough estradiol to trigger her maturation into a woman. Because she has no uterus, however, she does not menstruate. This may prompt her to go to a gynecologist, who will discover that she has no internal female organs, her vagina has a dead end, and she is carrying a pair of testes. The doctor will usually recommend removing the testes because they might turn cancerous, and then will prescribe estrogen replacement to substitute for the hormones that had been produced by the testes. If, as sometimes happens, the vagina is too short for comfortable intercourse, it can be stretched. Other than that - and the fact that she cannot have children - the XY woman is no different from an XX female. If anything, she's more likely to match the Western male standards of a beautiful woman, with long legs, well-developed breasts and clear skin. She could have a height advantage in sports or may become a fashion model, an occupation that supposedly holds a number of XY women, or a movie actress. Indeed, there are at least two well-known American movie stars who are XY women, according to researchers in sex differences, although neither of the actresses wishes her condition to be made public.
See also Maria's own account in the medical journal The Lancet.