🚀 go-pugleaf

In article <4fd9gs$ueu@ds2.acs.ucalgary.ca> kmuldrew@acs.ucalgary.ca (Ken Muldrew) writes:
>baez@guitar.ucr.edu (john baez) wrote:

>>I'm mainly interested in how many bits of information needed to create
>>a new organism are contained in the phenotype and NOT in the DNA.  This
>>seems to be a much trickier and less-studied question.    

>I'm still not entirely sure what you're asking, here. Perhaps if I
>phrase it experimentally, then you could elaborate. Let's say we take
>a two-cell embryo and split it. Then take the DNA from one cell and
>insert this into a one-cell embryo from an outbred line (ie. from a
>different mother). Wait for these "twins" to mature and then compare
>phenotypes. Maybe you could try using zenogeneic (from a different
>species) hosts for the DNA as well. 

>Are these the sort of questions you're getting at? 

The experiment you propose might help answer my question, but I think my
question is very difficult and possibly not very precise as it stands.
I don't really expect anyone to be able to answer it anytime soon, but I
find it interesting.  

Here's what I mean in concrete terms.  In the movie Jurassic Park the
idea is that scientists find the DNA for dinosaurs and use it to clone
dinosaurs.  The details are omitted.  Viewers ignorant of biology might
think that you just hand a biologist the genome of a dinosaur and then
they mix up a bunch of chemicals and it turns into a baby dinosaur. 
Of course it isn't quite like that.  There is no stage in the life
cycle of a dinosaur when all its information is in the DNA.

So what I'm wondering is this: given the complete genome of an organism, how
much *additional information* would you need to give someone for them to
be able to build a living copy of that organism?  

Here we disallow "cheating" by relying on existing organisms.  For
example, while I'm not sure, I suppose we could create a Siamese
cat from its genome with the aid of a one-cell embryo of a Persian cat
and a mother cat.  (Is that actually true?  Can we remove the
nuclear DNA of the one-cell embryo and substitute some other DNA without
ruining things?  Are the mitochondria of Siamese cats pretty much the
same as those of Persians?  Anyway, in my ignorance I imagine it's possible in
principle.)  Perhaps we could even create a zebra with the aid of a
one-cell embryo of a horse and a mother horse.  But here we are relying
on a lot of pre-existing infrastructure... or in abstract terms, a lot
of pre-existing *information* about how to turn a particular genetic
code into a living organism of that type.  

In other words: if we wanted to transmit instructions by radio to a
highly intelligent alien civilization, which would enable them to create
a human being, how many bits would the message have to be?   (Assume we
have already set up lines of communication and can understand each
other... actually this point is a bit subtle.)  The human genome has about
3 billion base pairs, each of which contains 2 bits before we apply
any data compression, so transmitting the genome takes only 6 gigabytes.
If we omitted the "junk DNA" (but see below!) we'd only need 600 megabytes.
But the information in the genome is not enough for the aliens to 
build a person!  I think it's possible *in principle* to figure out the
needed extra information someday and transmit it.  But I have little idea 
how much more information it is.

For example, say we tried to transmit intructions on how to create a
one-cell embryo, together with instructions on how this one-cell embryo
was supposed to be dealt with in order to get a baby organism.  Then
we'd have to give a lot of information about what the cell is like,
enough to be able to build a cell *from scratch*.  For all I know the
amount of information required for this is vastly more than the
information in the nuclear DNA.  After all, the nuclear DNA never builds
a new cell from scratch; only with the help of an existing cell.

>>It is a subject of debate as to whether these are really useless "selfish
>>DNA" whose only job is to reproduce itself, or whether it has an
>>undiscovered function in the organism.  I think people have estimates at
>>to what percent of DNA is this "junk DNA".

>It's pretty highly conserved, so calling it "junk DNA" is probably
>just due to the hubris of biologists, IMHO. 

I'd love to know more about that.  What are some hypotheses for what its
role might be?