The second model would reveal how an extra X chromosome
affected the male mice.
Autism appears in four times as many men as women, so scientists have long suspected that the X chromosome
contains relevant genes.
A gene that scientists have found to regulate X chromosome
activity in mice doesn't work in people, report researchers from the Johns Hopkins Medical Institutions in Baltimore.
These bits of RNA have a thing for X chromosomes
. At the appropriate time in development, they appear to coat the entire length of one of the X chromosomes
, which then condenses into a Barr body.
When the researchers analyzed the sperm in the X collection tube, they found that 85 percent had the X chromosome
, as desired.
Both groups of volunteers achieved lower scores on those measures than previously established standards for females with two complete X chromosomes
, the researchers note.
This result, also published in the March 20 Nature, strongly implies that cells tally their X chromosomes
by simply counting Xist genes, says Ashworth.
In another test, which Hamer had been chastised for not doing in the 1993 study, investigators examined the X chromosomes
of heterosexual brothers of the homosexual men.
In the 1960s, geneticists discovered that female mammalian embryos randomly inactivate one of their X chromosomes
. Although researchers are still not sure exactly why this occurs, many assert that X inactivation initially arose to prevent the genetic inequity that would result if females had a double dose of active X chromosome
In theory, because his mother's X chromosomes
carried no hemophilia genes, the boy had no chance of being born a hemophiliac.
The fetal cells are then tested to determine if they contain an extra X chromosome
. The genetic counselor explained that girls with Trisomy X often have speech delays in early childhood, may be slower to walk and develop motor skills, and frequently have learning disabilities.
"Today, the human Y chromosome contains less than 200 genes, while the human X chromosome
contains around 1,100 genes," said Wilson.