# How many possible different humans are there?

#### mikeph

I'm wondering in terms of genetics... and as a warning my biology knowledge is very limited

From a mathematical point of view, if there are 20,000 genes in the human genome, how do we calculate the number of possible humans that can statistically be produced (without mutation)?

eg. Does each gene correspond to one of A,C,G,T? In which case an upper limit would be 4^20000? Or is this totally wrong? I'm thinking in terms of very rough figures.

Maybe another approach to the question is in terms of DNA sequencing... if someone looks at my DNA, what chance is there that someone else will have the same result? Or that I have the same DNA as someone else?

Obviously some combinations will not work, but am I right in thinking that if any 2 of the 7 billion humans have a child, that there are real and quantifiable boundaries to the human genome that say, without mutation, that "there is a possibility of producing this offspring" with certain DNA, but you're never going to produce an ape- that is too far different from a human.

So there must be a finite number of genetically distinct humans that can be made from combinations of the present human genome... but how can this number be calculated?

Sorry for the ramble, any help much appreciated.

Related Biology and Medical News on Phys.org

#### mazinse

few errors in your post that need to corrected. The A C GT isnt a gene, They are bases. A gene is sequence of bases, could be really long or short. The permutations would be a lot more than you are thinking.

The 2nd problem is that just because you have a different gene, the result protein might not be that different.

#### Ygggdrasil

Gold Member
By sequencing the DNA from various individuals, scientists have found 15 million single nucleotide polymorphisms, 1 million short insertions and deletions, and 20,000 structural variants (The 1000 Genomes Project Consortium). Assuming each of these sites of variation has only two alleles and that none are synthetically lethal, this puts an estimate of the possible combinations from randomly assorting these variants at 2^(1.6x10^6) or 10^480000.

#### Ryan_m_b

Staff Emeritus
The question is poorly formed (no insult, ignorance is no bad thing when you strive to correct it). Consider that genetically identical twins are phenotypically different because of differences in their environment. Aside from this fact that genetics are the start, not end, of the answer there is no fixed number and variation of genes. Anyone can be born with gene duplications and/or mutations in those genes creating novel genotypes.

"How many possible different humans are there?"

### Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving