According to the highest estimates (Fausto-Sterling et. al., 2000) perhaps 1 percent of live births exhibit some degree of sexual ambiguity [1], and that between 0.1% and 0.2% of live births are ambiguous enough to become the subject of specialist medical attention, including surgery to disguise their sexual ambiguity. Other sources (Leonard Sax, 2002) create a narrower definition of "true intersexual conditions" and estimate the incidence as far lower, at approximately 0.018%.
In typical fetal development, the presence of the SRY gene causes the fetal gonads to become testes; the absence of it allows the gonads to continue to develop into ovaries. Thereafter, the development of the internal reproductive organs and the external genitalia is determined by hormones produced by certain fetal gonads (ovaries or testes) and the cells' response to them. The initial appearance of the fetal genitalia (a few weeks after conception) is basically feminine: a pair of "urogenital folds" with a small protuberance in the middle, and the urethra behind the protuberance. If the fetus has testes, and if the testes produce testosterone, and if the cells of the genitals respond to the testosterone, the outer urogenital folds swell and fuse in the midline to produce the scrotum; the protuberance grows larger and straighter to form the penis; the inner urogenital swellings grow, wrap around the penis, and fuse in the midline to form the penile urethra.
Because there is variation in all of these processes, a child can be born with a sexual anatomy that is typically female, or feminine in appearance with a larger than average clitoris; or typically male, masculine in appearance with a smaller than average penis that is open along the underside. The appearance may be quite ambiguous, describable as female genitals with a very large clitoris and partially fused labia, or as male genitals with a very small penis, completely open along the midline ("hypospadic"), and empty scrotum.
There are dozens of named medical conditions that may lead to intersex anatomy. Fertility is variable. The distinctions "male pseudohermaphrodite", "female pseudohermaphrodite" and especially "true hermaphrodite" are vestiges of 19th century thinking that placed "true sex" in the histology (microscopic appearance) of the gonads.
The common habit in the 21st century of elevating the role of the sex chromosomes above all other factors when determining gender may be analogous to the older habit of finding "true" sex in the gonads. Though high school biology teaches that men have XY and women XX chromosomes, in fact there are quite a few other possible combinations such as Turner syndrome XO, Metafemale syndrome XXX, Klinefelter's syndrome XXY, Jacob's syndrome XYY, Mosaicism XO/XY, de la Chapelle syndrome XX male, Swyer syndrome XY female, and there are many other individuals who do not follow the typical patterns (such as individuals with four or even more sex chromosomes).
Thus, people nowadays may be more likely to look towards the sex chromosomes than, for example, the histology of the gonads. However, according to researcher Eric Vilain at the University of California, Los Angeles, "the biology of gender is far more complicated than XX or XY chromosomes".[2] Many different criteria have been proposed, and there is little consensus.[3]
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Biological causes of intersexuality
Typical males have sex chromosomes XY and typical females XX. One biological definition of a male child is the presence of a Y chromosome. This definition has sometimes been used for sex determination at sports events, but it caused much confusion because it does not always apply.
The most common cause of sexual ambiguity is congenital adrenal hyperplasia, an endocrine disorder in which the adrenal glands produce abnormally high levels of virilizing hormones. In genetic females, this leads to an appearance that may be slightly masculinized (large clitoris) to quite masculine.
In many cases individuals are neither XX nor XY:
The presence of one or two additional X chromosomes in a male (XXY or XXXY) may cause Klinefelter's syndrome.
A single X chromosome (XO) is called Turner's syndrome. It is characterized by a lack or incomplete development of certain primary and secondary female characteristics and is associated with a range of medical issues.
Sex chromosomal mosaicism or chimerism can cause what was once called "true hermaphroditism", the presence of both testicular and ovarian tissue in one individual.
In Persistent mullerian duct syndrome the child has XY chromosomes typical of a male. The child has a male body and an internal uterus and fallopian tubes because his body did not produce Mullerian inhibiting factor during fetal development.
The following further XY cases leads to intersexuality:
Androgen insensitivity syndrome. They develop either partially or fully as females, due to their bodies failing to respond to testosterone. In the case of complete androgen insensitivity syndrome (CAIS), their tissues are totally insensitive to androgens, and they will develop as females, with normal female external organs. However, they will not develop a uterus or fallopian tubes, due to the production of Mullerian inhibiting factor by their testes. At puberty breasts will develop due to the production of estrogen by the testes; but no menstruation will occur due to the lack of a uterus. The tissues of individuals with partial androgen insensitivity, by contrast, have partial sensitivity to testosterone, but it is reduced compared to the male normal. These individuals can develop with either male external anatomy, or female external anatomy, or some combination, depending on the degree of insensitivity.
5-alpha-reductase deficiency. In this condition, individuals have testes, as well as vagina and labia, but with a small penis capable of ejaculation instead of a clitoris (this penis, however, appears to be a clitoris at birth). These individuals are normally raised as girls. However, come puberty, their testes will descend, their voice will deepen and they often will develop a male sexual identity. But they develop only limited facial hair. The number of people with this condition varies geographically, depending on how much of a given population is interrelated.
Excessive in utero exposure to androgens may lead to intersexuality in XX cases:
Congenital adrenal hyperplasia: Female internal anatomy, but ambiguous or male external genitalia, and develop male secondary sexual characteristics.
Progestin-induced virilisation. In this case, the male hormones are caused by use of progestin, a drug that was used in the 1950s and 1960s in order to prevent miscarriage. These individuals have internal and external female anatomy. They develop however some male secondary characteristics, and they frequently have unusually large clitorises.
A similar phenomenon occurs in cases where a cow brings two fraternal twins, one male and one female, to term. Because (unlike humans) such twins share hormones via their placental blood interface with the mother cow, male hormones produced in the body of the fetal bull find their way into the body of the fetal cow and masculinize her brain. The result is a freemartin (unconventional heifer), a cow that will eventually try to mount other cows the way that a bull would.
In XX male syndrome (also called de la Chapelle syndrome) the resulting child is usually a phenotypically normal male, but without sperm production. This syndrome is sometimes the result of an abnormal interchange of the SRY region from a Y chromosome to an X.
2006-06-24 16:51:02
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answer #1
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answered by Mac Momma 5
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Yes this is not "common" but happens quite a bit. Many people are born Chimera's (where their bodies merge with that of their twins in the first 1-4 days after cell division begins.) After the first week of cell division something like this would result in a "siamese twin" instead of a Chimera. Chimera's can often; if the "other twin" would have been Fraternal, have two genetic i.d.'s. Yes, one person with two different sets of dna. They will have pockets where one persons dna will be and another where anothers is dominant. The only way to tell is to test all of the major organs, blood, hair, skin, etc., denoting where each one resides. The intersex occurs when twins that would be male and female mix. Instead of a set of twins you get a single child with two sets of sex organs.
2006-06-24 16:55:52
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answer #6
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answered by AdamKadmon 7
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