In the new experiments, the mice lacked the gene because they didn't have
Y chromosomes. So the team substituted a similar gene from the X chromosome called Eif2s3x.
These genes are all over the human chromosome map; one of them is on the
Y chromosome. It has a homologue on the X that is not inactivated, so cells of normal males and females have two functioning copies of this gene, allowing them to make enough ribosomes.
``I wanted to show there were five or six
Y chromosomes circulating,'' he says.
In a study slated to appear in Molecular and Biological Evolution, Hammer and his colleagues trace the origin of the two Native American
Y chromosome lineages to a mountainous region of southern Siberia.
Without recombination between chromosomes,
Y chromosomes tend to degenerate.
In June, Forsberg's team reported linking
Y chromosome loss to a higher risk of several types of cancer and a decreased life span in a smaller group of men.
According to an international team of geneticists, about 1 in 12 men in Asia--and therefore 1 in 200 men worldwide--carry a form of the
Y chromosome that originated in Mongolia nearly 1,000 years ago.
For this reason, recent studies have attempted to utilize the paternally inherited
Y chromosome as well as biparentally inherited autosomal genetic markers to study the relatedness and histories of populations.
87), some of these eggs carry a
Y chromosome in, stead of an X.
The
Y chromosome data support several other DNA studies indicating that modern humans arose from a small number of Africans who lived from 100,000 to 200,000 years ago, Harpending says.
Just what might have happened to the
Y chromosome in XY females also interests Jennifer A.
Lyon suggested, for example, that females wouldn't inactivate an X chromosome gene if it had a counterpart on the
Y chromosome. In such a case, both sexes still would have two active copies of the gene in question.
