How many unique people does dna support?

[slayer202]

That probably isn't a very good way to pose the question but let me explain. There is a great richard dawkins quote

We are going to die, and that makes us the lucky ones. Most people are never going to die because they are never going to be born. The potential people who could have been here in my place but who will in fact never see the light of day outnumber the sand grains of Arabia. Certainly those unborn ghosts include greater poets than Keats, scientists greater than Newton. We know this because the set of possible people allowed by our DNA so massively exceeds the set of actual people. In the teeth of these stupefying odds it is you and I, in our ordinariness, that are here.

How big is this set of possible people? Do we have a figure on this? Did a quick google on my phone but no luck

 

[SunnyD]

Let us not forget nature versus nurture. DNA isn't the end-all be-all of a person.

The permutations that can be provided by DNA are finite, but may as well be limitless for our purposes. The number would be orders of magnitude larger than the population of all living things on this planet. And then take into account upbringing, desire, etc. all as intangibles that can make a person "great". The final solution is literally infinite.

 

[slayer202]

Of course not, I'm just curious about the number, I don't want to turn this into any sort of debate. I've read the quote many times and I always wonder

I'm sure it's a huge number. I suppose it's large enough to support millions and billions more years? Not that we're going to make it that far lol

 

[dullard]

That probably isn't a very good way to pose the question but let me explain. There is a great richard dawkins quote

How big is this set of possible people? Do we have a figure on this? Did a quick google on my phone but no luck

We could theoretically calculate a maximum upper limit. Take the number of base pairs in human DNA and calculate all the possible combinations of A, C, G, and T in all of those positions. Ignore for the moment altered DNA bases (which is how nurture can even affect DNA thereby affecting nature).

But, that would vastly over-estimate the number of possible humans. Why?
1) We don't use all of our DNA. How much we use is still a mystery. That is, how much of the DNA actually codes for proteins and the like that actually affect us? We don't know. Thus, we can't really begin to answer your question since we don't know how many DNA base pairs to put into the equation.

2) Some DNA changes don't affect proteins. For example the DNA sequece AAA and AAG both code for the same amino acid and thus the same protein. So, not all changes in DNA would change the human outcome. Thus the number of possible humans is decreased dramatically.

3) However, counteracting point #2, even if they code for the same protein, the protein might be built slower or faster with different DNA combinations. Thus, you might get more or less of the protein, or the protein may fold differently (be more or less active). So, even if a change won't affect the protein coding, it might affect the protein in other ways. Thus, to answer your question we'd need to know exactly how every single possible protein behaves in all possible permutations.

4) But, we can counteract point #3. Even if you do have two different proteins, the change may be buried in the middle in an unimportant part and thus you might have two different proteins that behave exactly the same way. Are these different possible humans, or are they the same possible human?

5) Etc.

Just speaking of the nature part of the equation, there are trillions of unanswered questions, so we can't even begin to give more than a rough estimate.

 

[slayer202]

I see. Awesome info though, thanks!

 

[Farmer]

It's difficult without actually knowing something about the subject. If you are talking about, how many different human DNA sequences there can be, you have to know exactly how many base pairs can vary between person and person.

An upper bound is simple: how many possible arrangements of base pairs can there be that make up a human DNA strand? HGP indicates 3164.7 million base pairs in human genome. 4 possible base pairs, so an upper limit would be

4^(3.1647e6) ~ 10^2000000

Which is mind boggling and not really useful. That's also a huge overestimate because 1.) obviously not all base pairs are variable, since 99% of the human genome does not vary between human to human and 2.) Certain differences in the gene sequence do not result in any noticeable difference in gene expression.

In other words, to pose this problem, you need to define clearly what you mean by "unique."

Looking up on Wiki: "Nucleotide diversity in humans" approximately 0.1%, which I approximate to mean ~3165 variable nucleotides, so from a nucleotide perspective, the ballpark figure is:

4^3165 ~ 10^2000

Human population is on the order 10^9, so, still mind boggling. While this is still an overestimate because not all nucleotide difference result in different expression, it is safe to conclude that we won't be seeing any "natural clones" in the near future.

EDIT: Uhh, so its actually a lot more, since 3.1647e6 != 3164.7 million. But same idea.

 

[silverpig]

Um, lots?

Remember, DNA is what makes spiders spiders. Is a 9 foot tall human still a human? What about a 20 foot tall human? What about one with 4 arms?

 

[slayer202]

Very very cool farmer, thanks

Um, lots?

Remember, DNA is what makes spiders spiders. Is a 9 foot tall human still a human? What about a 20 foot tall human? What about one with 4 arms?

True, surely we would be evolving before we ever got close to the "limit"

 

[DrPizza]

Are you saying that two twins are not unique individuals?

 

[dullard]

Farmer: 0.1% of 3.165e9 is not 3165.

Mistyped while correcting Farmer's typo.

 

[CPA]

I want 4 arms.

 

[Born2bwire]

Farmer: 0.1% of 3.165e6 is not 3165.

0.1% = 0.1*0.01 = 1e-3.

 

[Farmer]

Farmer: 0.1% of 3.165e6 is not 3165.

6-3=3, I believe I'm right. You can check on a calculator if you want.

 

[Scotteq]

I want 4 arms.

I'd rather have a prehensile dick... :awe:

 

[Born2bwire]

6-3=3, I believe I'm right. You can check on a calculator if you want.

Ah! But I don't think 3164.7 million is 3.1647e6. There! Now we have found fault in your post and can safely ignore all future statements and opinions by you.

 

[Farmer]

Ah! But I don't think 3164.7 million is 3.1647e6. There! Now we have found fault in your post and can safely ignore all future statements and opinions by you.

Ah shit.

 

[IceBergSLiM]

more than IPv4 and IPv6 combined

 

[SphinxnihpS]

Are you saying that two twins are not unique individuals?

Genetically, but one can be better in bed.

 

[dullard]

Genetically, but one can be better in bed.

Genetically twins are different. Nurture affects DNA. For example, a life experience can methylate a part of DNA (chemically react with it). That affects the gene that the DNA encodes. It can turn it on or off or increase/decrease its expression. Thus, not even identical twins are genetically the same.

 

[SphinxnihpS]

Genetically twins are different. Nurture affects DNA. For example, a life experience can methylate a part of DNA (chemically react with it). That affects the gene that the DNA encodes. It can turn it on or off or increase/decrease its expression. Thus, not even identical twins are genetically the same.

Link? Not doubting you, I'm just interested. Genetics has come a long way since I learned about peas.

 

[dullard]

Link? Not doubting you, I'm just interested. Genetics has come a long way since I learned about peas.

First Google link.

And that isn't the only part. Radiation is well known to affect DNA too.

 

[rasczak]

almost 7 billion so far?

 

[Born2bwire]

First Google link.

And that isn't the only part. Radiation is well known to affect DNA too.

Lord knows how much I nurtured my DNA working around that accelerator...

 

[Gigantopithecus]

Genetically twins are different. Nurture affects DNA. For example, a life experience can methylate a part of DNA (chemically react with it). That affects the gene that the DNA encodes. It can turn it on or off or increase/decrease its expression. Thus, not even identical twins are genetically the same.

Also, though twins are genetically identical at the moment of fertilization, once the zygote splits, different mutations immediately start accumulating in the germline cells of the two zygotes. Of course, the number of mutations that can reasonably be expected to occur in the two individuals is vanishingly small compared to the size of the entire genome, so for practical purposes they are the same, but technically, they are not.

Anyway, before any actual calculations are done, you need to answer a very basic question: what is a human? Is it the subset of creatures that are more genetically similar to each other than any is to, say, a chimpanzee? If that's the case, then you only need to consider how different we are from chimps to figure out how many different combinations of DNA could be more like each other than to a chimp.

 

[Acanthus]

You guys are calculating the upper bound for all possible life, not just Humans.

I don't even know where to begin for a correct solution, but that is a glaring error in the current calculations.