How many "unique" base pairs are there in the human genome?

Question

I've heard that a large fraction of the human genome is the same for all humans. What fraction is left over, i.e. how many base pairs are there that differ between most/all humans?

I wonder because I'm curious how many "possible" configurations (genetically speaking) there are for human beings.

I guess I should also add "meaningful" -- if we remove base pairs due to noise and common components, how many base pairs are left?

Answer 1

Nobody knows exactly. There are a lot of nucleotides to look at, and you need to look at them for a lot of people to really know whether you've got all the polymorphisms. But there are pretty good estimates: "any two unrelated people share about 99.9% of their DNA sequence" http://en.wikipedia.org/wiki/International_HapMap_Project .

We have 3×10^9 base pairs according to http://en.wikipedia.org/wiki/Genome , so that means about three million base pairs where people differ. But to know the number of possible combinations, you would need to know how many different alleles there are at each locus. If it was just two, there would be 2^(3x10^6). Roughly a one followed by a million zeroes.

Also, no one really knows whether DNA with no known function has no function, or whether it has one and we just don't know it.

Answer 2

The human genome has been sequenced, but not nearly a large enough sample size of people has been sequenced to estimate the overall polymorphism over the entire human population. I don't think a reasonable calculation could be done here. For all intents and purposes, though, the number of "possible" configurations is nearly infinity. We don't have a name for the number that large. We are talking on the order of millions of base pairs which would end up being 4 to the several millionth power.

Answer 3

It's a difficult question to answer, mostly because the answer isn't very meaningful. Well under half of the DNA in the human genome is significant; the rest is noise, left over from earlier evolution, so it could (and does) differ, but the differences don't matter.

Answer 4

even if you get a good estimate of 'single nucleotide' polymorphisms (i read recently about 10 million of these with a frequency of 1% or greater in the population) there are additional complications. novel mutations are always turning up - each new human has maybe 100 of these. and single base substitutions are not the only type of mutation - you can also have insertions, deletions, translocations...

the number of possible configurations really is astronomical. far larger than the number of people that have ever lived.

Answer 5

A. 3 Billion