How many Combinations of human DNA are there?

Question

How many Combinations of human DNA are there? I.e. how many templates of humans can be created? What is the chance that a another human can exist with identical DNA?
If the entire population of humans that have ever existed are taken to account, can there have possibly been an identical "me" ever in history?
(Obviously we disregard identical twins in this query)

Answer 1

The answer is not truly infinite, and disregarding identical twins is not necessary. The number of base pairs in human DNA is something on the order of 3 billion. Given that each base pair can be one of four combinations, the total combinations is 3 billion to the fourth power (i.e. 3B X 3B X 3B X 3B), so it's a big number. Given that 6B people live on the planet today, and that approximately 25000 generations of homo sapiens has existed (500,000 years divided by 20 years per generation, I figure about
150 Trillion humans have lived so far (somebody check my math here). So you can imagine that the possibility of a direct DNA copy of yours is very minute, and most likely never existed, and never will again.

Of course, this ignores population growth (from just a few to 6B) and make some very basic assumption. Also, natural selection and evolution have selected for some traits and against others which ensure that humans many generations ago didn't have some of the same genes that you have today, but again we are just doing a probabilistic determination here, not a genetic one. If we get into the genetic discussion, the probability of a direct copy reduces further significantly. We have also ignored the fact that DNA strands can also differ in their length. You may have a gene in your DNA that I don't even carry because it was cut out of my genome a few generations ago. For example, you may not have the gene that codes for the enzyme which digests lactose (or perhaps you are just missing the expression gene), making you lactose intolerant.

The reason that we don't have to discount identical twins is that even in identical twins, minute differences in the DNA of the two individuals still exist, since point mutations can be introduced with each DNA copy, which is a natural part of cell division. That what makes every individual unique in their DNA. Of course, these mutations may not occur in a gene which has a function which causes them to appear different, but often they do, causing such unique features as a twisted nose, small height differences, differences in athletic ability, muscle mass, desire to eat or drink (causing weight differences), moles, freckles, etc. So to a certain extent, some randomization, even in similar DNA sequences, makes us unique. Then there's the impact of environmental factors....but that's for another discussion.

The fact is, that for most of us, most of our DNA is very similar, and small differences make the differences between you and I. In fact, DNA differences between species can be surprising small as well.

Answer 2

Ur question hints at the answer;or rather an answer.

(And this is interesting, for it means that its likely that you
could almost choose,say, the most interesting!)

We, like science itself, wants to know whether the combinations-of-DNA are infinite or not; and,i think that
you and i here have to judge or rather take an estimate
between Infinity and not.

You also talk of "the entire population of humans...";
as if this is not increasing; as you know it is,along with
the Whole body of humankind(of whom we can agree
that the dead will always outnumber the living or existing).

For my answer, i think it is possible that an identical
"me" existed in history(and that its possible for an
identical "someone" to exist here on earth,now).

So the question is a good or reasonable one;like whether
there is true randomness from computors, (comparable
to the randomness of a true lottery).
So i think my answer, that we CAN put a definite number to
the combinations-of-DNA, could be challenged/criticised.

And this answer could could start from the basic templates
of male and female- a reasonable and different start point.

Answer 3

Too many crossover events occur during meiosis to ever allow two duplicate humans. Even if you ignored those, the odds of two siblings getting the same chromosomes from the same set of parents is 2^46, roughly 1 in 70,000,000,000,000.

Answer 4

32 x32 x32 helix combinations plus random factors of hard or soft connections, which will change with age or environment so a consistent change is taking place hence evaluation , so nobody can be the same as you

Answer 5

Infinite possiblilities, there are only similarities between members of the same family.

Answer 6

there are loads of combinations but all DNA is from a male or femal chromsone,

Answer 7

2, well if everbodys DNA is different what do you think the answer is?

Answer 8

en espanol there are mucho