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SRY

SRY is the sex-determining Y chromosome gene in humans and other primates, linked to determining males. It is not the only, or even most common sex-determining gene in mammals. Most non-primate mammals use the Y chromosome gene UBE1 for the same purpose.

The SRY gene encodes the testis determining factor, also referred to as SRY protein.

Here are proofs that SRY indeed determines maleness.

  • Humans with Y chromosome and many X chromosomes (XXY, XXXY etc.) are usually males.
  • There are males of XX karyotype. It turns out that these males have SRY gene in one or both X chromosomes, moved there by chromosomal translocation. (However, these males are infertile.)
  • Similarly, there are females of XXY karyotype. These females have no SRY gene in their Y chromosome. (Klinefelter’s syndrome)
  • Using genetic engineering, mice with XX karyotype but with SRY gene in one of their X chromosomes were made. These mice appeared to be male.

One of the most controversial uses of this discovery was “gender verification” used at the Olympic games, implemented by the International Olympic Committee in 1992. Athletes with SRY gene were not permitted to participate as females, although all athletes in whom this was “detected” at the 1996 Summer Olympics were ruled false positives and were not disqualified. In the late 1990s a number of relevant professional societies in United States called for elimination of gender verification, including the American Medical Association, the American Academy of Pediatrics, the American College of Physicians, the American College of Obstetricians and Gynecologists, the Endocrine Society, and the American Society of Human Genetics, stating that the method used was uncertain and ineffective (Facius 2004). The screening was eliminated as of the 2000 Summer Olympics.

Individuals with XY karyotype and functional SRY gene can have a female phenotype, where the underlying cause is Androgen Insensitivity Syndrome (AIS).

References