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What it does say is that the X and Y chromosomes are not as pure and pristine as people have believed. The SRY gene on the Y chromosome is believed to trigger the development of a male fetus, but we now see that the SRY can actually jump over to the X chromosome, which is why we have men with two X chromosomes.
It is also interesting to note that the researchers no longer present such intersex conditions as rare. One researcehr explains that their university has 70,000 students, so you must expect that at least 14 people to have a single X chromosome and 35 to 70 to have two X chromosomes and a Y. And they may not know it!
Recombination makes every individual unique, down to the last pair of sex chromosomes. Recombination occurs routinely everywhere except on the sex chromosomes, where the genetic deck of cards remains stacked, unable to shuffle information -- with the exception of two small regions located at the tips of the X and Y chromosome, called pseudoautosomal regions (PAR1 and PAR2). "The pseudoautosomal region, this tiny region that still recombines, is extremely understudied, typically filtered out of all analyses," said Wilson Sayres. In addition, there is a rogue island of the X chromosome, called the X-transposed region, or XTR, which was duplicated from the X to the Y around the last common ancestor of all humans. (...)
"This sex-determining region of the Y in the testis determining pathway, is now in humans, right next to the boundary," said Wilson Sayres. "The big implication is that because of the way our Y chromosome is structured, SRY is immediately next to the boundary, and because the boundary is fuzzy, we can get SRY hopping over to an X chromosome." SRY can be shuffled to the X, resulting in an increase in sex-linked disorders, such as a SRY positive XX males, known as de la Chappelle syndrome. "We know that large aspects of gender are really built on societal expectations, but it turns out that also our ideas of what sex is, genetically, may also be a little bit determined by public consensus. Sex has to do with if you are making eggs or sperm in humans. Sex, in fact, can be decoupled from your sex chromosomes. This fuzzy boundary makes it even more messy." Other fuzzy sex-linked boundaries include Turner syndrome (females with only one X), affecting one in 2,500 individuals, and Klinefelter's syndrome, found in one in a 1,000 individuals. Wilson Sayres, who specializes in computational biology, notes that despite what on the surface seem like rare conditions are not so rare if we changed our mindset.//
Last Edited By: jackmolay Mar 28 17 2:44 AM. Edited 1 time