X chromosome

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Related to X chromosomes: Y chromosomes

X chromosome

[′eks ′krō·mə‚sōm]
(genetics)
The sex chromosome occurring in double dose in the homogametic female sex and in single dose in the heterogametic male sex in mammals, Diosophila, and many other organisms.
References in periodicals archive ?
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 genes.
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.