Text 1333, 75 rader
Skriven 2005-01-04 20:31:00 av Perplexed In Peoria (1:278/230)
Ärende: Re: "GENES ARE FOLLOWERS
================================



"CNCabej" <cncabej@aol.com> wrote in message
news:crc4mn$21al$1@darwin.ediacara.org...

> "The direct specification of an
> arbitrary >>wiring pattern of 10^4 connections betwen 10^10 neurons in the
> human cerebral >>cortex would, for instance, take more than 10^15 bits of
> information. This is to >>be compared to the little more  than 10^9 bits in
> human genome."

> The authors deal with a specific problem: the source of the immense volume of
> information for synaptic MORPHOLOGY, concluding that the source is not
genetic,
> but epigenetic.

[Uses character graphics - view with a fixed-width font]

Perhaps a diagram will help to clarify just what the issues are:

                       Genome
                      /  |    \
    0.1 x 10^9 bits)-/   |     \-(0.9 x 10^9 bits)
                    /    |      \
          Housekeeping   |      CNS
                         |       |\
             (10^9 bits)-|       | \-(10^15 bits)
                         |       |  \
                         |       |   Morphology
 (Next generation)     Genome    |
                      /  |    \  |-(??? bits from CNS)
    0.1 x 10^9 bits)-/   |     \-|-(0.9 x 10^9 bits from Genome)
                    /    |      \|
          Housekeeping   |      CNS
                         |       |\
                         |       | \-(10^15 bits)
                         |       |  \
                         |       |   Morphology
                        ...     ...

Explanation of diagram:  According to your theory, the 10^9 bits
of the genome completely determine the housekeeping functions of
the organism, and they may also contribute (not sure what your
theory says here) to the determination of the CNS of the organism.
The CNS then determines the morphology of the organism - a process
that requires at least 10^15 bits of information.  I don't think
that anyone has a serious problem with what you are saying so far.

For the next generation, the original genome provides its 10^9 bits
to the genome of the next generation.  In addition, your theory
claims, the CNS of the first generation passes some number of bits
by epigenetic inheritance to the CNS of the next generation.  It
was my understanding that you were claiming that this epigenetic
inheritance channel carries something on the order of 10^15 bits.
Your critics claim that this is absurd.  Very few bits are passed
via the channel connecting the first generation's CNS to the next.

But then where do the critics believe that the 10^15 bits for
morphology come from, since the genome can only carry 10^9 bits?
I think that they would claim that these bits actually were
encoded (i.e. compressed) in the 10^9 bits of the genome.

In other words, although it may seem that there are 2^(10^15)
different ways of wiring the body, only a tiny fraction of these
are actually achievable by the processes of development.  So it
doesn't actually take anything like 10^15 bits to specify which
wiring diagram to use.  The 10^9 bits of the genome suffice.
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