  A nucleotides sequence is identified, in the two (four) letters alphabet, by
the the labels of a vector state of an irreducible representation of U_q(sl(2))
(U_q(sl(2) + sl(2))), in the limit q -> 0. A master equation for the
distribution function is written, where the intensity of the one-spin flip is
assumed to depend from the variation of the labels of the state. In the two
letters approximation, the numerically computed equilibrium distribution for
short sequences is nicely fitted by a Yule distribution, which is the observed
distribution of the ranked short oligonucleotides frequency in DNA. The four
letter alphabet description, applied to the codons, is able to reproduce the
form of the fitted rank ordered usage frequencies distribution.
