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Fwd: [anunda] The Sources of Instinct 2

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  • Christopher Wynter
    Message 1 of 1 , Nov 6, 1999
      >Two X chromosomes do not necessarily make a female,
      >according to recent research.
      >A researcher, Paul Overbeek, a professor of cell biology
      >at Baylor College of Medicine in Houston
      >created a strain of transgenic mice whose offspring
      >all turned out to be male, and every one of them
      >had a double X chromosome.
      >In other words, the X and Y chromosome combination
      >may not determine male gender.
      >Instead, the new research suggests that male gender
      >is determined by two genes, called Sry and Sox 9.
      >"Females are 'repressed' males and males are 'repressed' females,"
      >Sry is located on the Y chromosome and is the gene
      >that researchers believe normally determines male gender.
      >The researchers discovered that Sox 9 (female) is the gene
      >that regulates Sry (male) expression.
      >Researchers theorized that males either have some system
      >for turning Sry on or that females have a system for turning it off,
      >Research proved both theories to be true.
      >It turns out that the normal XX female does not express
      >Sox 9 because it is suppressed,
      >while the normal XY male gonad does express Sox 9.
      >"We eliminated the female ability to suppress Sox 9,
      >and as a result of that, the XX mice expressed Sox 9
      >and that is sufficient to get the normal pathway of male development to
      >even in the complete absence of a Y chromosome,"
      >Overbeek believes the same holds true for humans.
      >"Although it was known to be the critical gene on Y,
      >how it functioned was not yet so well established," Overbeek said.
      >The male XX mice were sterile,
      >which leads researchers to believe that germ cells --
      >those that make sperm -- are created by other genes located on the Y
      >Overbeek created the transgenic mice by injecting them with a gene
      >but had no inclination that their offspring would be males with two X
      >"The original intention was to make mice that had interesting mutations,"
      >"We just didn't know what we would end up with."
      >There is a significant obstacle to the research, however.
      >Since all of the offspring are male, the researchers can't breed them.
      >"Our transgenic family is not a stable genetic system,"
      >"You can't make females, so it's an evolutionary dead end."
      >The work could answer a long-pondered question:
      >Who came first, Adam or Eve?
      >"We don't know which came first even from our research,
      >but the system is set up so that the pathways for male or female development
      >are essentially encoded completely in the genome
      >of the male and female both.
      >One simple genetic switch sends the developmental program
      >in one direction or another,"
      >"Males and females are really very much genetically the same."
      >Christopher Wynter
      >Hobart Tasmania
      > * The information contained in this document is copyright.
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