Although many boys will start puberty normally, the extra
X chromosome interferes with the body's ability to produce testosterone.
These results indicate that there may be an undiscovered gene on the
X chromosome that affects sexual behaviours in mice and perhaps in other mammals, the researchers say.
The reason is that women can often compensate for a defective
X chromosome gene if the counterpart gene on their second
X chromosome is in working order.
In a female embryo, the choice of which
X chromosome to inactivate--either that from the mother or that from the father--is random in each cell.
In contrast, male fruit flies double the activity of their single
X chromosome.
The researchers divided their volun-teers into two groups: 55 with a complete
X chromosome inherited from their mother and 25 with an undamaged
X chromosome from their father.
Two new reports add to a growing body of evidence that an unusual gene called Xist may hold the key to
X chromosome inactivation.
Page and his colleagues suggest that this finding is at odds with theories that the Y chromosome, once it started evolving separately from the
X chromosome, only degenerated.
Two years ago, Hamer reported that men might inherit a predisposition to homosexuality through the
X chromosome, whose genes are passed on by mothers (SN: 7/17/93, p.
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.
Men have one
X chromosome and one male-determining Y chromosome, while women have two
X chromosomes.
An uncommon form of manic depression may be linked to markers on the
X chromosome, the NIMH scientists say in the April ARCHIVES OF GENERAL PSYCHIATRY.
