Epigenetics of Reproduction in Animals - Building the Most Complex Structure on Earth - page 85

In summary, it may be said that the signals from the nervous system are passed
along a cascade to the target cell, where the last signal of the cascade starts an intra-
cellular transduction pathway, which generally results in induction of the expression
of a specific gene or group of genes.
Genetic Versus Epigenetic Information
Genetic information is a product of random changes in genes (errors in the replica-
tion of DNA), i.e., it is determined by the thermodynamic factors of disorder and is a
manifestation of the natural trend of material systems to lose their original order and
increase their entropy. However, the random change, which represents loss of order
at the DNA level may serve as an acquisition of order at the cell level, i.e., it may
improve the function of the protein in the wider biochemical context of the cell. It is
in this context that the random, meaningless change—the error in the genetic text—
acquires “meaning” by improving the function of the protein. So, the loss of order at
a lower level of organization (the molecular level) represents an increase of order at
the higher level of the cell.
By contrast, epigenetic information is not a random product of thermodynamic
forces, conditions, or factors. Its generation is the product of the work, a product of
computation (data or information processing) in specific structures, microtubules (and
probably other structures) in unicellulars, and specialized neural tissue in metazoans.
Genetic information produces order at the molecular level by determining the
sequence of amino acid residues in protein molecules, but there is no evidence
that it can determine the order or the patterns of spatial arrangement of differ-
ent types of cells in the intricate histological structures of organs in multicellulars.
Development of these patterns requires huge amounts of data in the form of epige-
netic information.
Just like genetic information is continually transmitted to effectors to compensate
for lost proteins, epigenetic information is continually transmitted to target tissues
and organs to induce them to produce new components and cells to compensate for
relevant losses, thus maintaining homeostasis or restoring normalcy to the unavoid-
ably degraded biological structures.
As opposed to genetic information, which exists or is embodied materially in the
form of the sequence of nucleotides in DNA, epigenetic information is computed in
a structure, such as a nerve cell or neural circuit, and probably in the cytoskeleton of
all groups of living organisms, including unicellulars (see the sections “The Control
System in Unicellulars” and “Can the Cytoskeleton Compute?” in Chapter 1). It is
transmitted in the form of commands to particular structures, via neurohormonal
algorithms (signal cascades) or directly by the information-generating structures, to
produce a particular phenotypic result. Embodied in the structures of DNA, genetic
information is transmitted by the template mechanism of transcription involving a
one-to-one correspondence of nucleotides between molecules of DNA and mRNA
and a three-to-one correspondence between mRNA nucleotides and amino acids in
protein molecules during the translation process.