Caster Semenya and the Issue of Gender Ambiguity

The controversy over South African athlete Caster Semenya's gender has given the public a view into the complexities of gender. At first blush, the issue should be fairly straightforward: a person is either a male (with an X and a Y chromosome) or a female (with two X chromosomes). But the reality is that a number of conditions can blur the gender line.

After her 800-meter final on August 19 at the World Athletics Championships in Berlin, the International Association of Athletics Federations announced that they had asked Semenya to undergo tests to verify that she was female, with IAAF spokesman Nick Davies describing the tests as "extremely complex, difficult," according to the journal Nature http://www.nature.com/news/2009/090820/full/news.2009.850.html. (Scientific American is part of the Nature Publishing Group.)

Some people with two X chromosomes can develop masculine characteristics, whereas others with one X and one Y chromosome never develop masculine characteristics, Nature reports. Still, others (most notably, males who are XXY) defy conventional thinking of gender along the lines of XX females and XY males.

Some people with two X chromosomes have medical conditions that elevate androgen levels (which stimulate or control the development and maintenance of masculine characteristics); other people born XY fail to develop as men because of androgen insensitivity syndrome. Whereas XX individuals with plenty of androgens develop male characteristics, XY individuals who are not sensitive to it may grow up with female characteristics. This androgen-insensitivity makes gaining an athletic advantage through these conditions unlikely in most cases, Myron Genel, a pediatrician and expert in sexual development disorders at Yale University, told Nature.

About one in 4,500 babies show ambiguous genitalia at birth, such as a clitoris that looks like a penis, or vice versa, Scientific American reported in a 2007 article. In that story, geneticist Eric Vilain of the University of California, Los Angeles, noted that, lacking the Y chromosome, an embryo will follow the "default" genetic pathway that leads to ovary development, although "antimale" genes are required to make functioning ovaries.

The controversy has also spotlighted the taboos associated with someone who might share both male and female characteristics. (The IAAF has asked Semenya to undergo a number of complex gender tests, according to The Los Angeles Times, so any judgments about her gender are premature at this point.)

Semenya's case is not without precedent. At the 1996 Olympics Games in Atlanta, eight female athletes were determined to have XY chromosomes and were not allowed to compete, The Los Angeles Times reports, adding that further studies showed that they were physiologically female even though their genes said they were male, and they were reinstated. The Times article includes several examples of how genetics and gender don't always match.

Tetragametic chimerism
Tetragametic chimerism is a less common cause of congenital chimerism. It occurs through the fertilization of two ova by two sperm, followed by the fusion of the zygotes and the development of an organism with intermingled cell lines. This happens at a very early stage of development, such as that of the blastocyst. Such an organism is called a tetragametic chimera as it is formed from four gametes — two eggs and two sperm. Put another way, the chimera is formed from the merging of two nonidentical twins in a very early (zygote or blastocyst) phase. As such, they can be male, female, or hermaphroditic.

As the organism develops, the resulting chimera can come to possess organs that have different sets of chromosomes. For example, the chimera may have a liver composed of cells with one set of chromosomes and have a kidney composed of cells with a second set of chromosomes. This has occurred in humans, and at one time was thought to be extremely rare, though more recent evidence suggests that it is not as rare as previously believed. Most will go through life without realizing they are chimeras. The difference in phenotypes may be subtle (e.g., having a hitchhiker’s thumb and a straight thumb, eyes of slightly different colors, differential hair growth on opposite sides of the body, etc) or completely undetectable. Another telltale of a person being a chimera is visible Blaschko’s lines.

Affected persons are identified by the finding of two populations of red cells or, if the zygotes are of opposite sex, ambiguous genitalia and hermaphroditism alone or in combination; such persons sometimes also have patchy skin, hair, or eye pigmentation (heterochromia). If the blastocysts are of the same sex, it can only be detected through DNA testing, although this is a rare procedure. If the blastocysts are of opposite sex, genitals of both sexes are often formed, either ovary and testis, or combined ovotestes, in one rare form of intersexuality, a condition previously known as true hermaphroditism. As of 2003, there were about 30-40 documented human cases in the literature, according to New Scientist. Since hermaphroditic chimeras would be expected to be the one half of all chimeras, with purely male and purely female chimeras being one-quarter each, this would suggest that the condition is not particularly common.

Natural chimeras are almost never detected unless the offspring has abnormalities such as male/female or hermaphrodite characteristics or skin discolouring. The most noticeable are some male tortoiseshell cats or animals with ambiguous sex organs.

Chimerism can be detected in DNA testing. The Lydia Fairchild case, for example, was brought to court after DNA testing showed that her children could not be hers, since DNA did not match. The charge against her was dismissed when it became clear that Lydia was a chimera, with the matching DNA being found in her cervical tissue. Another case was that of Karen Keegan.[1]

The tetragametic state has important implications for organ or stem-cell transplantation. Chimeras typically have immunologic tolerance to both cell lines. Thus, for a tetragametic human, a wider array of relatives and other persons may be eligible to be an organ donor.[citation needed] Chimerism also shows, under a certain spectrum of UV light, distinctive marks on the back resembling that of arrow points pointing downwards from the shoulders down to the lower back; this is one expression of the Blaschko’s lines mentioned earlier.[2]

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