Monday, June 25, 2007

Genographic Project Update III

I have already written my understanding about the Genographic Project. Do not get confused by the word Genographic, DNA, Chromosome etc; rather read this one just as a discovery information, then it may be interesting.

I was reading an article in internet from the site of Genographic project, and came to know some interesting facts about human migration and thought sharing here.

Scientists agree that all humans share a common ancestry in Africa. Much less well understood is how the human race migrated from Africa and became so diverse. So far we know from the evidence of fossil and genetic data that human race was originated in Africa couple of hundred thousand years ago, few thousand individuals in Africa to six and half billion today all over the World.
The genographic project, which helps in analysis of DNA to track the ancestry roots have already reveled some interesting facts. Some of them I have mentioned in first post.

Here goes the analysis of DNA of an US born anthropologist Dr Spencer Well who is heading the project. He has common Y chromosome haplotype or set of linked markers that’s found through Southern England. If we go little bit further back, his ancestors were living down in Spain. This is during the worst part of the last ice age; that means 15000 years ago. If we go back to 35000 years ago, his ancestors were in Central Asia, and before that at around 40-45,000 years back they lived in Middle East; as part of second migration out of Africa; they were back n Africa along with everybody else, around 50,000 years ago.

As far the project can tell about two migrations from Africa, the second one was the major one we just discussed, was through Middle East around 45,000 years ago.

The first one took place probably around 50-55,000 years ago that took a southern coastal rout, so along with the south cost of Asia, southern India and ended up in Australia. Isn’t it amazing!!

This document has opened up some more information to me. I discussed that the ancestry root can be traced by Y chromosome, but for female I didn’t have any clue, but came to know about Mitochondrial DNA; what I still don’t know is how we can trace with this DNA, still searching for answers.


Dr Umesh R Bilagi said...

Since You have posted on Y chromsome I have problem in connection that
Please check out this
I read that size of Y chromosome has reduced because it did not have
partner at all. but X chromosome has not reduced, they say that it is
because, it has partner in female sex to recombine.
If Chromosome don't get partner to recombine than there is tendency to
delete genes which may be harmful produced by mutation. which intern
will reduce the size of chromosome is the logic.
Now if X chromosome gets only 50% chances to recombine then I think
size of X chromosome should also reduce to a size in between Y and its
initial size in reptiles
If gene deletion by natural selection if it is correct why there is
preservation of X chromosome size when it has only 50% Chance to
exchange with its real partner. It should also have 50% disadvantage.
How is this?
This is my guess. Please comment.

AJEYA RAO said...

Good Info there.

Kalyan said...

I came to know about the genographic project a year or two back through the National Geographic channel & it interested me immensely, though I was not into in depth study, but now I'm getting to learn more. The National Geographic website on Genographic project also provides a lot of information about this study. Isn't it very interesting to know our roots & the diversity!

Pijush said...

Dear Umesh,

Thanks for introducing me with this interesting subject. Though I am not a bio student, I find it extremely interesting and jotted down my understanding below. Please feel free to challenge me, so that I can learn more on this.

Y So Lonely?
Unlike the twenty-two pairs of autosomes, there is no recombination between the X and most of the Y chromosome. Genes on the part of the Y chromosome that does not recombine will be passed from father to son.. (First link)
The fact that it doesn't have a matching pair poses a bit of a problem for the Y chromosome.
Over time, mistakes have crept into the Y chromosome, too. But every time a gene on the Y chromosome went bad, it basically disappeared. Scientists theorize that the X and Y chromosome started out with about the same amount of genes -- about 1,000. Today, the Y chromosome has less than 80 genes. (Second link)

Hope for Y's Future
Some geneticists think the Y chromosome is now little more than a genetic wasteland that will eventually just disappear. If that were to happen, it would certainly spell the end of sexual reproduction. (Second Link)

Now your Question is “If gene deletion by natural selection if it is correct why there is preservation of X chromosome size when it has only 50% Chance to exchange with its real partner. It should also have 50% disadvantage. How is this?”

My analysis:
1)First of all X always has a pair in female. So it has not suffered the problem of recombination, thus able to hold most of the genes intact.
2)At this point of time Y lost most of the genes, so the only way to preserve the genes can be done through X, i.e, the size should be kept intact. This explains why X should be preserved.
3)I think it has nothing to do with the exchange, but I am not sure about it.
4)Having a single copy of any chromosome other than the X or the Y is lethal in humans; however, only one X chromosome is needed for normal development to occur. (First link)
May be this is the reason for the preservation of X.

I have not able to found the section in the website where it has described the preservation topic, will be helpful if you can provide me with the link of that section

Thanks again for coming here and sharing your thoughts.

With Rds,

Pijush said...

@Kalyan, I visited the NG site too and it also contains some interesting info. Another thing that I want to mention is one can participate in this project by submitting his DNA sample (however not free)

@Ajeya, Thanks

Anonymous said...

woow it is fun to imagine our ancestors in middle east and africa!!
some scholars say japanese language is rooted from african language too :)
coz there are so many words in common.

Raghu Ram Prasad said...

your collection is very beautiful and very intersting........thanks for giving good information

Raghu Ram Prasad said...