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WHAT DOES IT MEAN TO BE TRANSGENDER? 7 sex chromosome (45,X or 45,Y, also referred to as 45,X0 and 45,Y0), some have three sex chromosomes (47,XXX, 47,XXY, etc.), and some males are born 46,XX and some females 46,XY. In most cases, the chro- mosomal makeup of an individual matches with their external appearance and sense of gender identity, but this is not true for everyone. One reason people outside the medical community may be aware of the existence of chromosomal variants is the publicity afforded to the cases of some female athletes who were disqualified from competition due to their nonstandard chromosomal makeup. Typically, these athletes had lived their entire lives as females and had never had any reason to suspect that there was anything unusual about their bodies and yet were not allowed to compete as women due to a lab test indicating their chromosomal makeup was something other than 46,XX. Because we now recognize that gen- der has social and psychological aspects, and that there is more variety in chromosomal makeup than was previously believed, the simple statement that females are XX and males are XY is no longer accepted in the scien- tific community. Some variations in chromosomal makeup are common enough to have been studied in detail. Persons with Turner syndrome (45,X) are pheno- typically female, meaning that their observable sex-based characteristics are those associated with females, although they are sterile, tend to be short, and lack prominent female secondary sexual characteristics. Per- sons with three X chromosomes (47,XXX) are taller and more slender than average, have normal development of female sexual traits, and are fer- tile. Individuals with Klinefelter syndrome (47,XXY) are phenotypically male but infertile, produce small amounts of testosterone, and have incom- pletely developed male secondary sex characteristics. Males with the XXY makeup have higher than usual amounts of testosterone, are taller than average, and are usually fertile. Even if an individualÊs chromosomes are 46,XX or 46,XY, a medical condition may affect the way inherited sex characteristics are expressed. For instance, individuals born 46,XX (typically female chromosomes) with congenital adrenal hyperplasia (CAH) will have a deficiency of cor- tisol, which may result in incomplete female sex differentiation and an outwardly male appearance. Individuals born with typically male chro- mosomes (46,XY) but who have androgen insensitivity syndrome (AIS) will develop external female genitalia and breasts because their body does not respond to androgens (male hormones) but does respond to estrogen (a female hormone). Such individuals are likely to have been raised as females and to have a female gender identity, despite having the chromo- somal makeup typical of a man.