Computing vs. Genetics - Advancing Artificial Intelligence Through Biological Process Applications - page 170

Of course, none of the machines mentioned
here have, as far as we know, been built, but
there is nothing to stop them from being built.
Scientifically, nothing stands in the way of their
construction. Whether it is technologically fea-
sible to make replicas is another question, and a
tricky one at that.

ally, n-ary when A is formed by, respectively, two,
three or, generally, n symbols. If all the words are
of the same length, C is said to be a fixed-length
or block code. Otherwise, C is said to be a vari-
able-length code.
Let σ be the alphabet of a source of information,
which is defined as the source that emits symbols
of an effect σ {

}

,... s s , whose probability of ap-
pearance is given by (

5

1

)

≤1 . Then a coding
is an application ϕ of σ in C, which is extended
to an application ϕ* of σ* in C*. And, of course,
decoding is an application ψ of C* in σ*. A code
has only one decoding, i.e. ϕ* is injective, and ψ
or ψ* is the identity.

i ≤ r

i

GENETIC CODE

Code vs. Cipher

Technically, a code is defined as a substitution at
the level of words or sentences, whereas a cipher
is defined as a substitution at the level of letters.
Ciphering means concealing a message using a
cipher, whereas coding means concealing a mes-
sage using a code. Similarly, the terms decipher
is applied to the discovery of a ciphered mes-
sage, i.e., in cipher, whereas the term decode is
applied to the discovery of a coded message. As
we can see, the terms code and decode are more
general, and are related to both codes and ciphers.
Therefore, these two terms should not be confused
through misuse. For example, Morse code, which
translates the letters of the English alphabet and
some punctuation marks to dots and dashes, is
not a code in the sense of a form of cryptography
because it does not conceal a message. The dots
and dashes are simply a more convenient form
of representing the letters for telegraphy. Really,
Morse code is nothing other than an alternative
alphabet.
Code is formally defined as follows. Let A* be
a free monoid (Hu, 1965) engendered by the set
A, i.e. A* is the set of finite-length words formed
by means of concatenation (the associative law
of internal composition) with the symbols of A
and with a neutral element, namely, the empty
word. A code {

Genetic Code

The expression genetic code is now used to mean
two very different things. The lay public uses it
often to refer to the full genetic message of the
organism. Molecular biologists use it to allude
to the small dictionary that shows how to relate
the four-letter language of the nucleic acids to the
twenty-letter language of the proteins in the same
way as Morse code relates the dots-and-dashes
language to the twenty-six letters of the alphabet.
Here we will use the term in this sense. However,
the technical term for such a rule of translation
is not, strictly speaking, code but cipher, just
as Morse code should be called Morse cipher.
This Crick did not know at the time, which was
a stroke of luck, as genetic code sounds much
better than genetic cipher . In actual fact, Crick
correctly referred to the set of bases contained
in the chromosomes as ciphered text or key, but
added that the term key or ciphered text was too
limited. The chromosomal structures are at the
same time the instruments that develop what they
foresee. They represent both the legal text and the
executive power or, to use another comparison,
they are both the architect's plans and the builder's
workforce.
Code is the core of molecular biology just like
the periodic table of elements is at the heart of

} C c = , then, is a subset of

A*, where the elements of ci i are the words of the
code and n i denotes the size of the word ci. i .
A code is said to be binary, ternary or, gener-

1 ,...,

i