Friday, April 01, 2005

Women are more (genetically) complex than men

With the recent completion of the human genome project, scientists are starting to use that information to answer some fundamental questions about our species. Recently, major breakthroughs have been made in researching the X chromosome, and Nature magazine has published some startling findings: women are actually more genetically complex than men. It turns out that women, whose gender are established by two copies of the X sex chromosome (one from mom and one from dad), were originally thought to silence one copy to prevent conflicting versions of genes found on the X chromosome from wreaking havoc on their bodies. Men, on the other hand, having only one copy of the X chromosome (which they got from mom), just expresses all the genes on there without a care in the world. Well, it seems the research group has found that things aren't as simple as all that. Women will actually express a number of genes from both copies of their X chromosome, and for genes in which only one copy is expressed, it can differ between different women which of their two X chromosomes is getting expressed and which is getting silenced. The net effect is that there is greater variability within women than within men. This could also be a genetic explanation as to why women and men might be different in behaviour and physiology.

Women get extra dose of X-chromosome genes Data may help to explain differences between women and men. Although men and women may often act like separate species, scientists have long believed they are really not that different when it comes down to their DNA. But now, researchers have found that the sexes differ more than we thought, particularly when it comes to the genes on one crucial chromosome. Every woman carries a double dose of the X chromosome, whereas men carry one X and a Y. Women don't express both copies of the X chromosome in their cells: in each cell they shut one copy down (the 'inactive' X) and use the other. However, it seems that the inactive X doesn't just sit down and shut up. The first of two research papers on the human X chromosome, both published in Nature, analyses the complete sequence of the hromosome1. The second shows that women still express many genes from their inactive X chromosomes2. What's more, different women express different genes from the inactive X.

Taken together, the two papers may eventually explain some of the behavioural and biological differences between individual women, and perhaps, between women and men. Quietly active Scientists already had an idea that the inactive X chromosome is not completely silenced. But they did not realize just how active it actually is. Hunt Willard of Duke University in Durham, North Carolina, and Laura Carrel of the Pennsylvania State College of Medicine in Hershey, investigated this by designing tags that bind to messages from X-chromosome genes. The tags allowed scientists to pinpoint which genes were escaping inactivation. Using these tags to probe samples from 40 women, Willard and Carrel found that 15% of the genes on the inactive X chromosome were active in every sample. Another 10% of genes from the inactive X were switched on in just some of the samples. "The data are so striking," says Willard. "Every female is expressing a different subset of X-linked genes at different levels."

Because the genes expressed from the inactive X are also expressed from a woman's active X, women get a higher dose of these genes than men. So these genes may underlie traits that differ between the sexes. The scientists caution, however, that they have only investigated one type of cell, and that to draw any general conclusions the findings must be repeated in other kinds of cells. "It doesn't provide evidence that genes explain the differences between men and women, but it does provide candidates for such genes," Carrel says.

Cancer therapy The X-chromosome sequence, which is now 99.3% complete, has also revealed a few surprises of its own. The international team that assembled the sequence found that about 10% of X genes belong to a family (the 'testis-antigen genes') that has been linked to cancer. These genes are promising targets for potential therapies, because they are only expressed in cancer and in the male reproductive organs. Therapies that knock out issues expressing the testis-antigen genes should leave patients' other organs intact. Other key findings from the X sequence could help us understand how the chromosome evolved, and how it sends the signals that shut down the inactive chromosome. Investigating these leads will keep scientists busy for a long time to come, says genomicist Jenny Graves of the Australian National University in Canberra. "Having the quantitative picture of the X is absolutely new, and I think this gives us a really good picture of the whole X chromosome," Graves says.

Not that if they do find that women are genetically different than men that this should be any sort of stupid rationale for saying women are inferior to men or, god forbid, 'genetically better suited for child-rearing and housework', as one mysoginist once tried to tell me.


Blogger phillyjay said...

I read about this earlier, but from a different article
"Genetically speaking, women are complex and men are simpletons
By Maureen Dowd"

Some what tounge in cheek and a little silly, but some other blogs took it seriously, and are complaining about the liberal bias which is probably true.But then again, everyone has a bias view and won't be too quick to call someone out if they have the same political leanings.Either way it's not proven completely true yet, and if it is it won't change much.

4/01/2005 07:53:00 PM  

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