Fwd: I always knew they were different

[Harry Edwards]

Begin forwarded message:

> From: Harry Edwards <laughingwolf at EV1.NET>
> Date: March 17, 2005 10:58:02 AM CST
> To: GHETTO2 at LISTS.WHATHELPS.COM
> Subject: I always knew they were different
> Reply-To: Remembrances of Austin Ghetto <GHETTO2 at LISTS.WHATHELPS.COM>
>
>
> http://www.latimes.com/news/science/la-sci- 
> xchromosome17mar17,1,6092863.story?coll=la-news-science
>
>
> THE NATION
>
> Women Are Very Much Not Alike, Gene Study Finds
>
> X chromosome diversity among females suggests that in effect 'there is  
> not one human genome, but two -- male and female,' researcher says.
>  By Robert Lee Hotz
>  Times Staff Writer
>
>  March 17, 2005
>
>  Scientists have found genetic evidence for what some men have long  
> suspected: It is dangerous to make assumptions about women.
>
>  The key is the X chromosome, the feminine sex chromosome that all men  
> and women have in common.
>
>  In a study published today in the journal Nature, scientists said  
> they had found an unexpectedly large genetic variation on the X  
> chromosome among women. The findings were published in conjunction  
> with the first comprehensive decoding of the chromosome, which  
> appeared in the same journal.
>
>  Females can differ from each other almost as much as they do from  
> males in the behavior of many genes at the heart of sexual identity,  
> researchers said.
>
>  "Literally every one of the females we looked at had a different  
> genetic story," said Duke University genetics expert Huntington  
> Willard, who co-wrote the study. "It is not just a little bit of  
> variation."
>
>  The analysis also found that the obsessively debated differences  
> between men and women were, at least on the genetic level, even  
> greater than previously thought.
>
>  As many as 300 of the genes on the X chromosome may be activated  
> differently among women than among men, said molecular biologist Laura  
> Carrel at Pennsylvania State University College of Medicine, the other  
> author of the paper.
>
>  The newly discovered genetic variation among women might help account  
> for differing gender reactions to prescription drugs and the  
> heightened vulnerability of women to some diseases, experts said.
>
>  "The important question becomes how men and women actually vary and  
> how much variability there is in females," Carrel said. "We now might  
> have new candidate genes that could explain differences between men  
> and women."
>
>  All told, men and women may differ by as much as 2% of their entire  
> genetic inheritance, greater than the hereditary gap between humankind  
> and its closest relative — the chimpanzee.
>
>  "In essence," Willard said, "there is not one human genome, but two —  
> male and female."
>
>  Scientists estimate that there may be as many as 30,000 genes in the  
> chemical DNA blueprint for human growth and development known as the  
> human genome.
>
>  The genes are parceled out in 23 pairs of rod-like structures called  
> chromosomes contained in every cell of the body.
>
>  The most distinctive of the chromosomes are the mismatched pair of X  
> and Y chromosomes that guide sexual development.
>
>  Until now, researchers considered the shuffle of sex chromosomes at  
> conception a simple matter of genetic roulette.
>
>  The chromosomes that dictate sexual development are mixed and matched  
> in predictable combinations: A female inherits one X chromosome from  
> each parent; a male inherits an X chromosome from his mother and a Y  
> chromosome from his father.
>
>  To avoid any toxic effect from double sets of X genes, female cells  
> randomly choose one copy of the X chromosome and silence it — or so  
> scientists had believed.
>
>  The new analysis found that the second X chromosome was not a silent  
> partner. As many as 25% of its genes are active, serving as blueprints  
> to make necessary proteins.
>
>  To investigate this variation, Carrel and Willard isolated cells from  
> 40 women and measured the activity of hundreds of genes to see whether  
> those on the second X chromosome were active or silent.
>
>  Although those extra genes were supposed to be turned off, they found  
> that about 15% of them in all female cells were still active, or in  
> the terminology of genetics, "expressed." In some women, up to an  
> additional 10% of those X-linked genes showed varying patterns of  
> activity.
>
>  "This is 200 to 300 genes that are expressed up to twice as much as  
> in a male or some other females," Willard said. "This is a huge  
> number."
>
>  Researchers were surprised that they found so many unexpected  
> differences in the behavior of the one sex chromosome that men and  
> women share.
>
>  Though there is dramatic variation in the activation of genes on the  
> X chromosomes that women inherit, there is none among those in men,  
> the researchers reported.
>
>  Researchers have yet to understand the effect of so many different  
> patterns of gene activation among women or determine what controls  
> them, but all the evidence suggests that they are not random.
>
>  "What had looked like a simple yes or no has turned into a thousand  
> shades of gray," said molecular biologist David Page, an expert on sex  
> evolution at the Whitehead Institute for Biomedical Research in  
> Cambridge, Mass.
>
>  Illuminating this complex palette was the work of an international  
> team of 250 scientists led by geneticist Mark Ross at the Wellcome  
> Trust Sanger Institute in Hinxton, England. The team produced the  
> first complete sequence of the X chromosome about two years after the  
> decoding of the male Y chromosome.
>
>  The researchers found that the X chromosome, though relatively poor  
> in genes, is rich in influence, deceptively subtle, and occasionally  
> deadly to males.
>
>  The international team identified 1,098 functional genes along the X  
> chromosome, more than 14 times as many as scientists had located on  
> the tiny Y chromosome.
>
>  Even so, the researchers said, there were fewer genes to be found on  
> the X chromosome than on any of the other 22 chromosomes sequenced so  
> far.
>
>  Most of the X genes are slightly smaller than average. But one is the  
> largest known gene in the human genome, a segment of DNA linked to  
> diseases such as muscular dystrophy that is more than 2.2 million  
> characters long.
>
>  The X chromosome contains a larger share of genes linked to disease  
> than any other chromosome.
>
>  It is implicated in 300 hereditary disorders, including color  
> blindness, hemophilia and Duchenne muscular dystrophy. Nearly 10% of  
> the genes may belong to a group known to be more active in testicular  
> cancers, melanomas and other cancers, the team reported.
>
>  "The biggest surprise for us was just how many of these  
> [cancer-related] genes there are on the X," Ross said. "There are very  
> few of these elsewhere on the genome."
>
>  The complete gene sequence provided some clues to the origins of the  
> human sex chromosomes.
>
>  The researchers found that most of the genes on the X chromosome  
> reside on chromosome 1 and chromosome 4 of chickens.
>
>  That supports the theory that the human sex chromosomes evolved from  
> a regular pair of chromosomes about 300 million years ago when  
> chickens and humans shared a common ancestor.
>
>
>  If you want other stories on this topic, search the Archives at  
> latimes.com/archives.
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