Piero Scaruffi(Copyright © 2013 Piero Scaruffi | Legal restrictions )
These are excerpts and elaborations from my book "The Nature of Consciousness"
The process of “epigenesis” is the process by which the genotype is turned into the phenotype.
DNA is translated into another kind of polymer, RNA (ribonucleic acid), which is also a four-letter code (adenine, guanine, cytosine, uracil) while RNA, in its turn, is translated into yet another kind of polymer, the protein, whose units are aminoacids. There are twenty kind of aminoacids, so technically a four-letter code is translated into a twenty-letter code.
The way this works is by triplets of DNA units: three DNA units (which can each be of four different kinds, for a total of 4x4x4=64 combinations) is translated into one of the twenty aminoacids (some triplets generate the same aminoacid).
But the translation is more complex as DNA is a one-dimensional structure (a string) whereas a protein is a three-dimensional structure (it's the stuff that our flesh and bone and blood are made of). So the one-dimensional string of instructions of the DNA is used to determine the three-dimensional shape of a protein.
In summary, the DNA is the sequence of instructions for building molecules called proteins, and proteins are manufactured of amino acids, whose order is determined by the DNA. Note that our genome has only 30,000 genes, but our body has 100 trillion cells.
As far as the individual goes, we know that her genome is a synthesis of the genome of the parents plus some random shuffling. But it is not clear yet how much of the final individual is due to the genome and how much to the interaction with the environment. For example, the genome may specify that a muscle must grow between the arm and the trunk, but exercise can make that muscle bigger or smaller. For example, the genome may determine some psychological characteristics of the individual, but study, meditation and peer pressure can alter some of them. The British biologist William Bateson thought that only the genome mattered: we are machines programmed from birth. The US psychologist John Watson, on the other hand, thought that conditioning could alter at will the personality of an individual: it all depends on experience, the instruction contained in the genome is negligible.
There is also a subtle difference between which genes are in the genome and which genes are actually “expressed”. For example, the Israeli physician Moshe Szyf (“Maternal Care Effects On The Hippocampal Transcriptome And Anxiety-Mediated Behaviors”, 2005) found evidence that the early experience of the child affects the future psychological life of the child not only because it is stored in memory but also because it determines how some genes will be expressed. Szyf observed physical differences in the hippocampus of rats that account for differences in behavior, and he argued that those differences were caused by the way their mothers raised them. Rats who were raised in similar ways by their mothers tend to have the same kind of hippocampus. He credited this development to the expression of some genes as opposed to others. Maternal care seems to affect the chemistry within the cell that determines if and when those genes are expressed.
The role of RNA is probably underrated. Protein-encoding genes might be in the minority. Many different kinds of RNA exist and some kinds of RNA regulate the life of many protein-encoding genes. The number of protein-encoding genes seems to be mostly the same for all animals, from flies to humans (in the range of 20-30,000). However, the number of genes whose RNA performs other functions vary wildly among species. RNA acts as a simple "messenger" only in simpler organisms. RNA acts more like a “manager” in complex organisms, i.e. its "regulating" activities are much more widespread.
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