How many genetically distinct possible humans are there?

[Borodog]

Title says it all. I have no idea how to go about calculating this, but I would like to know a reasonable order of magnitude. Anyone have any clue?

[DougShrapnel]

I have no clue. Does Count by Gene (http://www.gdb.org/gdbreports/CountGeneByChromosome.html) help. 3 million base pairs and 30,000 genes.

[David Sklansky]

Well over a googol. Well under a googolplex.

[MexKrax]

Before answering this you need to be more precise about what you mean by "genetically distinct." If you count humans whose genomes differ even by a single base pair change then every human on Earth will be genetically distinct from one another, and every human ever born or who will be born.

There are about 3 billion base pairs in the human genome each one could have 4 different bases. If you assume that 10% of the genome is so important that changing it would result in lethality (and I think this is probably a high estimate) then you're down to only 2.7 billion base pairs that can have one of 4 nucleotides. So a rough guess would be there are 4^2 700 000 000 possible "genetically distinct" humans.

[Borodog]

Close enough. Thanks.

Seems much simpler than I thought it would be. I'm almost dubious. But I can't think of how you might be wrong.

[Rduke55]

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I have no clue. Does Count by Gene (http://www.gdb.org/gdbreports/CountGeneByChromosome.html) help. 3 million base pairs and 30,000 genes.

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It's not just the 30,000 genes. A lot of huge differences are due to the noncoding regions that influence and control gene expression. Many scientists think that's the main source of the differences between people (and even species).

[FortunaMaximus]

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Less a googol. Well under a googolplex.

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There are more than raw numbers involved here. The possibilities for genetic divergence slam the upper limit down quite a bit.

Unless you want to consider a mass of cojoined twins a race within their own right, with their cultural identities.

Could be interesting though.

[Nielsio]

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How many genetically distinct possible humans are there?

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0

Do you see why?

[theblackkeys]

Related question.

People say that no two people are the same (assume genetically speaking), not counting identical twins. This is not necessarily true, because two random people COULD, although not likely, have the same genes. Am I wrong?

[madnak]

The Earth could spontaneously turn into a giant pineapple.

Yes, it's hypothetically possible - but so is everything in science. I don't know the precise likelihood of two people on Earth being independently genetically identical. But it's very small.