Epigenetics of Reproduction in Animals - Building the Most Complex Structure on Earth - page 64

Genetic Information
Conventionally, genetic information is any sequence of bases in DNA (RNA in
some viruses), but here I will consider the term to include only those sequences that,
through processes of transcription and translation, can produce a polypeptide chain
in the appropriate conditions that per se , or together with other polypeptide chain(s),
can function as a functioning protein in the organism from which it derives. In this
context, genetic information is representative of a polypeptide chain.
The conventional wisdom that assigns genes other functions above the molecular
level is not warranted by the available biological evidence and is based on guesses.
In strictly scientific terms, we still have no mechanism showing how a gene or a
group of genes may determine the sequential stages of the development and evolu-
tion of a morphological, behavioral, or life history character. Studies on the con-
sequences of gene mutations or lack/inactivation of genes in the development of
such characters prove that these genes are necessary, but fall short of suggesting that
they may be sufficient for the development of these characters; many nongenetic
components are also necessary for the development of those structures, and in their
absence, these structures do not develop (or develop with defects). More than half
a century of unprecedented, intense research on the function of genes failed to pro-
duce evidence that any specific gene is responsible for the development of a supra-
molecular phenotypic character. No one has ever successfully demonstrated steps by
which a gene or a number of genes, per se , lead to the formation of a morphological
character.
The genetic information, thus, determines the sequences of amino acid residues in
the polypeptide chains; hence, it represents “meaningful” or semantic information,
as opposed to information in the communication theory, sensu Shannon.
Genes contain semantic information for protein biosynthesis alone, and recent
developments in biology show that most proteins in vertebrates are produced by
alternative splicing (AS), an epigenetic rather than genetic phenomenon (see the sec-
tion “Alternative Splicing,” later in this chapter). In this context, the idea that genes
also represent morphological structures or contain information for their development
is untenable. That could reasonably be claimed only if it was demonstrated that non-
genetic factors are not involved in the process of the development of these structures,
which obviously is not the case. Rejecting the idea that genes may contain semantic
information for phenotypic characters, Shea (2007 ) believes that genes have what he
calls “correlational information.” But one could easily argue that epigenetic struc-
tures such as acetylated histones and chromatin marks in general, as well as DNA
methylation/demethylation, also contain correlational information of the type he
envisages.
From the opposite position, it has been argued that if genetic information is
embodied in phenotypic structures, then the information of the relevant phenotypic
structures, according to communications theory, will equal the information for the
genetic structure that instructed the formation of the phenotypic structure. According
to this theory, the information in the phenotype is equal and symmetrical to the
information of the genotype and is such whether the information is in the receiver
or the sender. This is causal information that shows that the state of the sender and