

Light-Years of DNA - signa11
http://calculatedimages.blogspot.com/2015/04/light-years-of-dna.html

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nsxwolf
All the humans who have ever lived (~107 billion) created DNA just a bit
longer than the diameter of the observable universe (93 billion light years).

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ekianjo
How do you define when Humans started to live, though ? Evolution is not a
black and white process, we did not suddenly become humans and stopped being
apes. It was probably very progressive and gradual.

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jerf
At this scale, a factor of magnitude or two is of little consequence, and odds
are, you can get general buy-in within a "factor of magnitude or two" of the
number of humans to live from the vast bulk of people who might have sensible
opinions.

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SomeStupidPoint
In this case, it's actually very easy to get a good estimate: 10 billion is
too low, 1 trillion seems a little high, 10 trillion is definitely too high;
100 billion is, as such, really the only good estimate.

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zxyzzxxx
I remembered from school that the cell division limit is about 50 and evidence
( read: Wikipedia ) suggests that as well.
[https://en.wikipedia.org/wiki/Hayflick_limit](https://en.wikipedia.org/wiki/Hayflick_limit)

A tenth of a light-year is still impressive.

Even more interesting is the fact that the single cell organisms living in a
human body, outnumber human cells by a factor of 10.

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astrodust
There are exceptions, like immortal cells.

[http://en.wikipedia.org/wiki/Henrietta_Lacks#Legacy](http://en.wikipedia.org/wiki/Henrietta_Lacks#Legacy)

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fasteo
And then, we should add the "length" of our mitochondrial DNA. Although it is
much smaller than nuclear DNA (16.000 base pairs), every cell has between 100
and 10.000 copies of this mtDNA.

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pflanze
I was wondering about what "two copies" meant. Chromosome pairs aren't copied
from each other, but surely the author didn't mean to separate the DNA strand
into its mirrored halfs, that must surely not be stable whatever you do.

The first reference given doesn't open without cookies enabled, so I looked it
up on wikipedia instead [1]. The 3 billion number is the sum of the number of
base pairs of all of the different chromosomes; i.e. the size of the genome
data set that's (roughly) identical across all humans. So yes, one cell then
instead has the sum of the number of base pairs of chromosomes 1..22 times
two, plus the size of X * 2 or X + Y, which is approximately 2 * 3 billion.
Thus the calculation is correct.

[1]
[https://en.wikipedia.org/wiki/Human_genome](https://en.wikipedia.org/wiki/Human_genome)

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earljwagner
That's a long linear distance in a small volume. I'm reminded of space-filling
curves in math: [http://en.wikipedia.org/wiki/Space-
filling_curve](http://en.wikipedia.org/wiki/Space-filling_curve)

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valarauca1
>Most amazingly it would not be a light-year of random DNA sequence, but ten
thousand trillion identical copies of your DNA, faithfully replicated by your
cells.

Cell reproduction is a pretty imperfect.

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arrrg
From all I know DNA replication has a very low error rate. I’m not a
biologist, so I lack the expertise to accurately judge papers about this
topic, but the one I found (through looking the topic up on Wikipedia)
suggests a very low error rate:

“In total, these three discrimination steps result in an _in vivo_ mutation
rate estimated to be […] less than one error for every billion (or more) bases
pairs copied […]”
[http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3639319/](http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3639319/)

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michaelhoffman
Your diploid genome is roughly six billion base pairs. That means six errors
per duplication. But there will also be other errors introduced by DNA damage
from other sources, and processes which have evolved to modify your genome
(for example, V(D)J recombination).

