Although Jeanne thought that her baby-to-be was being tested for Down syndrome or other significant disabilities, her obstetrician phoned her to let her know that the fetus had a high probability of having Trisomy X, or an extra X chromosome
in a female.
The second model would reveal how an extra X chromosome
affected the male mice.
The X chromosome
may to many people connote femaleness, since women have a pair of X chromosomes
and men have an X and a Y.
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.
The reason female mammals bother inactivating an X chromosome
Women typically have two X chromosomes
, one inherited from each parent; men receive an X chromosome
from their mother and a Y chromosome from their father.
The genetic activity of a single X chromosome
is sufficient for a human cell, but women must somehow deal with a double dose.
Scientists believe this male chromosome once had thousands of genes in common with the X chromosome
, the other mammalian sex chromosome.
In a reprise of the most controversial study of 1993, researchers surveying the genetic landscape of the X chromosome
have discovered further evidence that it contains a gene or genes that may steer some men to homosexuality.
While the X chromosome
contains genes that direct a broad range of functions, such as blood clotting and some aspects of color perception, the Y chromosome for the most part bears only those genes responsible for male sexual characteristics.
Goodfellow of the Imperial Cancer Research Fund in London, England, and his colleagues have successfully moved a telomere -- the specialized structure that keeps the tips of chromosomes from unraveling -- up toward the center of the long arm of a mammalian X chromosome
It involved a boy with hemophilia A, an inherited bleeding disorder caused by a defective gene on the X chromosome
Several research teams had previously found the markers -- one for color blindness, the other for anemia -- among many people in other families with manic depression, and had proposed that as many as one in three manic depressives has a predisposing gene in that region of the X chromosome
(SN: 3/28/87, p.
Although further studies are needed to confirm the gene's exact function, its discovery -- coupled with the concurrent identification of a similar segment on the X chromosome
-- should answer some fundamental questions about what determines sex in humans and other species.
Evidence is mounting that, in some cases of manic depression,there is a gene near one tip of the X chromosome
that predisposes its bearers to the disorder.