Biomedical Engineering Reference
In-Depth Information
or elements or, so to speak, primordial genes. The
important point is that human genes should not
be considered as completely different from each
other. Rather, they should be seen as families
that live all sorts of lives. Having completed the
table, structural genetics will leave the field open
to functional genetics or the practical use of the
table. For example, the difference between two
people boils down to no more than 1% of the bases.
Most genes have only two, three or four variants,
that is, some 300,000 principal variants.
Going back now to deciphering the genome,
sequencing the genome refers to solely stating
the bases A, T, C and G of the genome, i.e. read-
ing without understanding. Therefore, it is to
spell out or, at most, babble the genome. For the
time being, genome sequencing simply involves
determining how the thousands of millions of
bases of which it is composed are chained. As
Daniel Cohen (1994) said, who we follow in this
section, it is not hard to realise how arid the task
is, as it involves examining a text that more or
less reads as follows:
threshold and start to understand what they are
reading. Reality is, however, much tougher, and
the deciphering of the genome looks like a very
hard and thankless task. This is due not so much
to the poverty of the alphabet but to the ignorance
of the language.
Just to give an illustrative example of what
we have just said, try to read, albeit for no more
than twenty minutes, and aloud (no cheating!),
a novel written in a language you don't know
(Turkish, Serbo-Croatian, etc.) transliterated to
the twenty-six letter Latin alphabet and see what
a headache you get. Suppose now that you have
no choice, because you are on a desert island and
the only topic you have is written in one of these
languages and you do not have dictionary on hand.
Therefore, you would have to make do with what
little you know and be patient and perseverant. If
you do this, you will end up becoming acquainted
with some features of the unknown language. For
example, you will identify recurrent patterns,
establish analogies, discover some rules, other
meanings, interesting similarities, etc., etc., etc.
The first thing we find is that the genetic language
has a peculiarity, which, at least in principle, is
disconcerting: it does not just consist of sequences
furnished with a precise meaning, the sequences
of interest which are called genes. It all includes
jumbled paragraphs situated both between gene
and gene, intergenes, and inside the genes, intra-
genes, which divide the meaningful sequence. To
date, no one has been able to find out what all this
filling is for. And, what is even more exasperating
is that these extravagant series of letters make up
over ninety per cent of the genome, at least, the
human genome, which is an interminable list of
genes and intergenes with non-coding intragenes
situated within the very genes.
Now consider a volume of poetry by Quevedo
(1995), but written in an unknown language
and according to the following genomic style,
although for the readers' comfort, the text has
been translated into Spanish:
TCATCGTCGGCTAGCTCATTCGACCATCG-
TATGCATCACTATTACTGATCTTG...,
and goes on for millions of lines and thousands
of pages. Of course, it was to be expected that
a language that has a four-letter alphabet would
be much more monotonous than contemporary
languages, whose Latin, Cyrillic alphabets, etc.,
are composed of over twenty letters.
But sequencing the genome is not the last stop,
as it has to be deciphered, i.e. its meaning has to
be understood like learning to read letters and
converting them into ideas. And this is the tricky
thing. There is, in actual fact, no way of foreseeing
when, how and to what extent it will be possible
to decipher the sequenced genome. It would be
marvellous, but not very realistic, to suppose that
learning to read the genome would unexpectedly
lead to its understanding just as children learn
the letters and suddenly cross some mysterious
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