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THURSDAY, Jan. 22 (HealthDayNews) -- Here's a cheerful finding for those who say that males push females around too much: On the molecular level, it appears male genes may have to leave their homes for protection, researchers report.

"Home" is the X chromosome, which plays a key role in determining the sex of the carrier. A female has two X chromosomes, while a male has one X and one much smaller Y chromosome. Studies in mice and humans show an unusually large number of genes can jump from the X chromosome to non-sex chromosomes, a research team at the University of Chicago reports in the Jan. 23 issue of Science.

That finding contradicts two beliefs widely held by geneticists, explains study leader Manyuan Long, an associate professor of ecology and evolution.

It has been thought that gene traffic is no greater for the X chromosome than for all the other genes, which are called autosomes. "That's just not true," Long says.

And standard theory holds that the X chromosome is the site of action for most sex-related genes. The Chicago studies show that many of the genes that leave the X chromosome are involved in male sexual development, and they may go elsewhere to do what they have to do.

At the moment, this is an exercise in pure, basic science. But it might someday provide useful insights into treatment of male sexual problems, since many of the jumping genes are involved in sperm formation, says J.J. Emerson, a member of the research team.

"This helps us understand which particular genes are likely to be involved in spermatogenesis," Emerson says. "So we can infer that anyone looking for genes involved with sperm formation can look at our genes."

As every schoolboy knows, chromosomes carry the genes that carry the information for production of the proteins that enable a living organism to live and grow.

Growth means the production of new cells, and therefore of new chromosomes. A human, for example, starts as a single cell, which divides to form two cells, which divide to form four, and so on. At each division, a complete set of chromosomes is produced for each new cell.

But the chromosomal production line is not perfect. Changes occur -- changes that can result in the new traits that are essential for the evolution of life. And those changes can include the transfer of a gene from one chromosome to another.

"What we see is that when genes are copied from one chromosome to another, the copying from the X chromosome is excessive," Emerson says. "The explanation is that natural selection is responsible for this excess."

There are two possible reasons why this occurs, he says, and both of them are based on the weakness of males -- at least at the genetic level.

One is that a male carries only a single X chromosome, and therefore it is less likely that a male-helpful gene will be able to do its work. By jumping to an autosome, the male gene increases its chances of being productive.

"The other explanation is sexual antagonism," Emerson says. "We would expect that female genes would have more of a say on the X chromosome. If so, and they don't care about male genes, in those cases where it would benefit females at the expense of males the only way for a male gene to work is to escape from the X chromosome."

If that explanation is correct, the war between men and women is being waged molecule against molecule. And at that level, it is the male who is weakest.

More information

A basic guide to genetics can be found at the National Library of Medicine or the National Human Genome Research Institute.

(SOURCES: Manyuan Long, Ph.D., associate professor, ecology and evolution, University of Chicago; J.J. Emerson, Ph.D, research assistant, University of Chicago; Jan. 23, 2004, Science)

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