It will also shed light on humanity's shared evolutionary history. "We will learn some more about…the period of a few hundred thousand years or so in which modern humans evolved before they spread from Africa," Durbin says. "This can be studied by looking for evidence of selection in the pattern of variation seen in the genome."

It is already clear that 99 percent of DNA is the same in all humans. But by mapping variations in the other 1 percent, the 1,000 Genomes Project may help reveal the genetic underpinnings of some disease. "Once you have those elements fingered, then you can figure out how to do therapies," Brooks says. "It's not going to tell you the causal ones, but it's going to give you the list of suspects."

3 Comments

1. 1. ecarturo 06:06 PM 1/25/08

   I've wondered this since Biology class in high school and the thought's come back to haunt me now with this article: How is it "clear that 99 percent of DNA is the same in all humans" when not all humans have been sequenced? Which part of the DNA was used as the *approximation*?

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2. 2. okarpe2 10:27 PM 10/23/09

   That's a good question! You are right, it can't be absolutely clear, but it turns out that the probability of picking two humans whose genomes are 99% the same by pure chance is nearly zero. Let's see why.
   
   Suppose we have a species whose genome is only 100bp long. Suppose the first individual of this species, whose genome we just sequenced, has genome of 100 As: AAAAA...AAAAA. Then we sequence the genome of another individual of this species. This one has TAAAA...AAAAA, that is 1 T and 99 As. Apparently these two are 99% similar.
   
   One may say, "so what? maybe it's just a coincidence." Well, it may be coincidence, but what the chances of that are?
   
   There are only 300 genomes that are 1 bp different from all As. These are TAA...AA, CAA...AA, GAA...AA, ATA...AA, ACA...AA, AGA...AA, and so on. 3 possible differences at each of 100 positions. 3*100=300.
   
   Now the total number of all possible genomes is astronomical: 4^100. Any of the four nucleotides (A, T, C, G) at each of 100 positions. The probability to blindly pick an individual whose genome is 99% similar to a given genome is 300/4^100 that is basically zero.
   
   That's why having sequenced genomes of only 2 individuals and observing a 99% similarity one may safely conclude that "99 percent of DNA is the same in all humans."
   
   I hope this explanation helps. Have a good day!

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3. 3. Quinn the Eskimo 02:56 AM 6/29/10

   So, let me see if I have this right. If you were to check two people's phone numbers, and they both live in, say, California, then all phones on the planet are located in the U.S.?
   
   DNA can prove you DID NOT do something.
   
   Proving you DID do something has an error rate.
   
   ecarturo is right. DNA statistics have a way to go to become irrationally true.
   
   Oh, eye witnesses are often wrong too.

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