Secrets of the X chromosome, revealed!

March 16, 2005 10:26 PM

Female X chromosome 'cracked' - "The discovery, by an international consortium of scientists, shows that females are far more variable than previously thought and, when it comes to genes, more complex than men." Nature reports two new studies; one on the complete sequencing of the X chromosome for humans, which sheds some light on how sex evolved and how women differ from men, and another on how women express many genes from X chromosomes previously thought dormant.
posted by kliuless (31 comments total)

The discovery, by an international consortium of scientists, shows that females are far more variable than previously thought and, when it comes to anything, more complex than men.
posted by puke & cry at 10:30 PM on March 16, 2005

btw, in light of the summers' brouhaha over his speculation on women's intelligence in certain fields -- that some phenotypic traits may be genetically innate or predetermined to some extent -- i thought it was also interesting that a stanford genetics professor recently found 326 genetic markers [abstract] that can be used to accurately classify people into common 'racial' groupings; resurrecting that old bogeyman of eugenics and human enhancement :D
posted by kliuless at 10:32 PM on March 16, 2005

That bit about the genetic differences between races is interesting. I always wondered how anyone could think that there isn't a genetic basis for race. The fact that Asians have children with epicanthic folds and African-Americans have children with dark skin isn't an accident over and over again. I think that a genetic basis for race is not "evil", it's just that the idea was put to such horrible use by groups like the Nazis that it became stigmatized and caused people to consciously avoid it.
posted by Sangermaine at 10:49 PM on March 16, 2005

*giggles at Puke & Cry...
posted by schyler523 at 11:09 PM on March 16, 2005

Sangermaine writes "I always wondered how anyone could think that there isn't a genetic basis for race."


The overall average genetic variance between any two "races" is less than the average variance between randomly selected individuals within a "race". That is, race tends to effect only that handful of genes concerned with the outer envelope of the individual: skin, hair, eyes, etc., with the vast majority of genes not concerned with that outer envelope going unaffected.

Blood groups, for example, while at different proportions within different "races", can be found in all races. So too most other human variation.

"The fact that Asians have children with epicanthic folds and African-Americans have children with dark skin isn't an accident over and over again. "

No, it's not an accident: non-black children, in Africa (without access to modern technology), die earlier from skin cancers, and so have fewer children, so evolution "rewards" black skin in Africa, just it "penalizes" black skin in Europe with rickets from lack of vitamin D. Similarly, in colder Europe a longer nose serves to pre-heat air, but in humid and high-altitude Africa, a wider nose makes breathing easier.
posted by orthogonality at 11:29 PM on March 16, 2005

True, orthogonality, but I feel the larger truth is that the concept of "race" itself is flawed - there aren't 6 or 7 races, there are hundreds, with mixes of all the "telltales" of a certain race. Here's one with dark skin and a flattened nose BUT light, smooth hair! Here's one with epicanthic folds BUT caucasian skin color and low cheekbones! There is a continuum of races and as such the genetic basis of said races is also a continuum. There is a genetic basis for race, yes, but the differences are so shallow that there is little need to concern oneself with them, aside from the things like, is it sickle cell anemia? that black people are resistant to, and so on.

As for the differences between the sexes - I'm all for searching them out. I happen to agree with Summers' hypotheses on that subject and any scientific explication of these discrepancies is welcome.
posted by BlackLeotardFront at 11:41 PM on March 16, 2005

What do we mean we ask about genetic differences between races and sexes? Given any scheme of grouping people into two or ten or one-hundred groups, there will be genetic similarities within the groups and differences between. For some schemes of grouping the differences will be greater, for some they will be less. It is not surprising that there is a genetic difference between what we usually think of as white people and black people- after all, skin color itself is genetically determined.

The question is, what are the implications of dividing people up in such a way? Obviously when we talk about races, we are talking about something other than the particular genetic traits in common for a group - historically people have tended to think a person's race says something about that person more than just their likelihood of getting sickle-cell anemia. How and why did society decide that skin color was the salient marker of group membership, and how has that structured inequalities within our society? You can't pretend that race is an objective idea.

For sex things are trickier, because the genetic differences between men and women are typically more specific. But there are ambiguities here too, lots of examples of people who don't fit out expectations of sexed bodies, and I don't think it is beyond the pale to ask, why in our society, is it so important whether or not someone has a penis?
posted by mai at 12:00 AM on March 17, 2005

NB about race - historically, people from different countries in Europe did not all consider each other White. Especially Italian and Irish immigrants to the US were looked down on in a racist way by other European immigrants. That only changed during the twentieth century.
posted by mai at 12:02 AM on March 17, 2005

The overall average genetic variance between any two "races" is less than the average variance between randomly selected individuals within a "race". That is, race tends to effect only that handful of genes concerned with the outer envelope of the individual: skin, hair, eyes, etc., with the vast majority of genes not concerned with that outer envelope going unaffected.
I was just noting that there were differences. Yes they are small overall, but they're there.

True, orthogonality, but I feel the larger truth is that the concept of "race" itself is flawed - there aren't 6 or 7 races, there are hundreds, with mixes of all the "telltales" of a certain race.

Actually, the "326 genetic markers" link that kliuless gave contradicts that:
"According to Neil Risch, PhD, a UCSF professor who led the study while he was professor of genetics at Stanford, the findings are particularly surprising given that people in both African-American and Hispanic ethnic groups often have a mixed background. "We might expect these individuals to cross several different genetic clusters," Risch said. This is especially true for Hispanics who are often a mix of Native American, white and African-American ancestry. But that's not what the study found. Instead, each self-identified racial/ethnic group clumped into the same genetic cluster."

Their findings indicate that there are four general genetic cluster groups, despite what we would imagine are mixings of hundreds of different groups.

As for the the implications of establshing such groups...I don't know. From a scientific standpoint it's fascinating, for instance, that within the "Asian" group you have two distinct "Chinese" and "Japanese" groups, while none of the other groups have sub-groups. Also, it seems like it could help in medicine, allowing treatments to be better targeted to a person's needs and make-up. Socially, though, it seems like this would either not matter or have negative implications, as I'm not sure what a positive social result of it would look like.
posted by Sangermaine at 12:28 AM on March 17, 2005

"What are you talking about? We're all the same, don't you dare imply we are not. Who gives you funding? Let me just make a phonecall...."

It may just be sarcasm, but that's in effect what happens when anyone wants to poke around in these areas, scientifically. Sad, but true.
posted by nightchrome at 12:51 AM on March 17, 2005

Race-specific genetically-modified virus coming up in 3... 2...
posted by Chunder at 1:37 AM on March 17, 2005

Sangermaine, I just meant along the lines of phenotypes the concept of race is a continuum. Genetically it's more distinct as you point out. It certainly is an interesting field of research, implications of its findings are far-reaching and diverse (so to speak).
posted by BlackLeotardFront at 2:01 AM on March 17, 2005

NB about race - historically, people from different countries in Europe did not all consider each other White. Especially Italian and Irish immigrants to the US were looked down on in a racist way by other European immigrants. That only changed during the twentieth century.

The last few times I filled out one of those ethnicity forms in Europe there were still two boxes to choose from: White and White-Irish.
posted by fshgrl at 2:14 AM on March 17, 2005

Where was this? Ireland?
posted by dabitch at 2:40 AM on March 17, 2005

A conventional chromosome in a forebear of humans -- probably a reptile of some sort -- apparently underwent a mutation that allowed it to direct the development of sperm-producing testes.

I wonder if there isn't a bone in these findings that will choke the Fundamentalists... if the X chromosome is more complex and the Y chromosome is a degraded copy of the X, then how was Eve created after Adam?

Oh, wait, I forgot, Fundies don't believe evidence.

Everybody believes in something and everybody, by virtue of the fact that they believe in something, use that something to support their own existence.-Frank Zappa
posted by Enron Hubbard at 3:28 AM on March 17, 2005

Where was this? Ireland?

UK. I think it was for EU stats though. Don't get me wrong, it didn't bother me at all, I just thought it was funny and kind of showed the idea of what constitutes a race is pretty situational.

Fundies don't believe evidence.
I don't think they believe in chromosomes either.
posted by fshgrl at 4:17 AM on March 17, 2005

if the X chromosome is more complex and the Y chromosome is a degraded copy of the X, then how was Eve created after Adam?

Let's not forget that men also have an X chromosome as well -- females just have a full pair of them. To create Eve, I can easily imagine a very tiny God working hard to join pairs of X chromosomes together with very tiny slivers of scotch tape, for instance, and then using the leftover Y chromosomes to assemble whale penises or something. My spiritual contacts tell me that the process is similar to working with Legos.

And isn't it obvious that modern genetics was invented by the devil to test the faithful?
posted by DaShiv at 4:40 AM on March 17, 2005

The overall average genetic variance between any two "races" is less than the average variance between randomly selected individuals within a "race".

The same is true of all measures of gender. On all measurable points there is greater variation within each gender than between the two genders.
posted by Miko at 6:49 AM on March 17, 2005

The language in these articles is so weird.

From the Nature link:

Although men and women may often act like separate species...

However, it seems that the inactive X doesn't just sit down and shut up.

From the Washington Post:

She was slow to reveal her secrets, but the X chromosome has now bared it all.

...falls far short of explaining all the mysteries of what makes a woman.

"It's more evidence that it's not so much what you've got as how you use it," said Mark Ross...

Is this tongue-in-cheek?
posted by nobody at 8:19 AM on March 17, 2005

Is this tongue-in-cheek?

You mean swab in cheek right?
posted by srboisvert at 8:31 AM on March 17, 2005

Really, decades of research catches up with common sense and every-day experience?

Does this finally get us past the ignorant assertion that the only difference between men and women is their reproductive organs?

Oh but now we know why. Ok fine whatever, welcome to reality.

But yeah, there's got to be major concern here for sure. Gender differences are common to all and a shared experience for all tribal, economic, national, religious, etc groups.

What scares me big time is the next step on this stuff. Already mentioned are 'racial' issues and what unethical leaders can accomplish with that.

Here's what I think is even worse: the stereotyping of individuals based on their genetic makeup. Can the day be far off when peoples lives will be pre-determined to a greater extent than now. Are we gonna find a 'music' gene and insist on that career path, are we gonna find a lack of the 'math' gene in some and deny financial support for higher education? How about insurance? Denied to those with genetic predisposition to disease? Or maybe a 'criminal' gene? Yikes.
posted by scheptech at 8:33 AM on March 17, 2005

I think they already found the criminal gene
posted by fshgrl at 8:41 AM on March 17, 2005

Okay, I just read "Genetic Structure, Self-Identified Race/Ethnicity, and Confounding in Case-Control Association Studies " by Tang et al. which spawned the discussion here on the biology of race. Genetics, and more specifically, statistics, is not my field, but I have a few observations from the article which may be helpful.

1) The study asks the question: If an American identifies herself as a member of group A, what is the likelihood that she is genetically similar to other Americans who identify themselves as group A, and dissimilar to people who identify themselves as groups B, C, D, E?

The study specifically focused on ethnicity in America. Their conclusion suggests that African Americans are genetically different from Euro Americans. They did not ask whether African Americans are genetically different from Africans, and their conclusions are not that African Americans are more "African" than "American" genetically speaking. That is, it could be that African Americans are far closer to Europeans than Africans, but still distinguishable from Euro Americans.

2) This study supports the idea that "race" is constructed by factors other than genetics: social restrictions on intermarriage and ancestral geographic seperation, for instance. They conclude

Therefore, researchers performing studies without racial/ethnic labels should be wary of characterizing difference between genetically defined clusters as genetic in origin, since social, cultural, economic, behavioral, and other environmental factors may result in extreme confounding (Risch et al. 2002).

3) The study concludes that in order to distinguish between groups, researchers must use a large number of genetic markers. This suggests to me that the similarities between "races" are far more frequent than the differences.
posted by carmen at 8:50 AM on March 17, 2005

don't know what your trying to say miko. What measurable points?
The overall average genetic variance between men and woman is huge- Y is one sixth the size of X
science is finally realizing you can't conclude how a woman's body will react (to drugs, environmental poisons, etc.) by testing men.
The basic signs for a heart attack are much different for women then men. the list goes on and on.
would like to see the differences acknowledged w/o assholes jumping to the conclusion "woman's brains are no good at math", and so on down the list of stupid things people say to excuse the real world effects of prejudice.
posted by pointilist at 9:02 AM on March 17, 2005

Science advances a little bit today.....however, not enough to justify the sweeping generalizations that I am seeing in some of these comments.

There are genetic differences between the races and sexes. Quantitative differences, not qualitative.

We're still all part of the same species.
posted by mygoditsbob at 9:22 AM on March 17, 2005

nightchrome, the idea that people who research into these areas can't get funding is one of the most ludicrous myths floating around these days. These are well-funded and well-researched areas of biology.
posted by kyrademon at 10:03 AM on March 17, 2005

Everyone seems to be happy that the X chromosome and women are more complex than men.

Are we really sure that complexity in and of itself is better? I would rather make my omelet in a pan that using a Rube Goldberg device.

It is the characteristics of the complexity and the way it works that makes for positive or negative value, not the existence of complexity itself.
posted by nathanrudy at 12:14 PM on March 17, 2005

nathanrudy writes " Everyone seems to be happy that the X chromosome and women are more complex than men. Are we really sure that complexity in and of itself is better?"

Boys have X chromosomes too. Women are more complex only insofar as some genes on one of their two X chromosomes are not wholly inactivated, as previously thought.

See Dawkins, The Ancestor's Tale, pp. 149-152, for possible positive effects for females of having two alleles of one gene. (But in his example, in different cells, not the same cells. Briefly, lucky females with be trichromats, while all males and some females will be dichromats, and each type of dichromat is able to find one color of food, but trichromats are able to find both colors of food.)
posted by orthogonality at 3:36 PM on March 17, 2005

On the issue of "race" please allow me to repeat this and you say it after me: race is a political construct.
Think homo sapiens. (except for the wing nuts, of course)

To the subject of genetics and women, who said they would never figure out females? Complex, yes, but impossible, no.
posted by nofundy at 5:28 AM on March 18, 2005

"Baby, i love you. You're so...compleX."

"Get away from me, you S.C.U.M.!"
posted by gorgor_balabala at 9:52 AM on March 18, 2005

fwiw, here's a talk with armand leroi on the nature of normal human variety :D

"Of course, there will be people who object. There will be people who will say that this is a revival of racial science. Perhaps so. I would argue, however, that even if this is a revival of racial science, we should engage in it for it does not follow that it is a revival of racist science. Indeed, I would argue, that it is just the opposite."

cheers!
posted by kliuless at 10:00 AM on March 25, 2005