  A mathematical algorithm to describe DNA or RNA sequences of $N$ nucleotides
by a string of $2N$ integers numbers is presented in the framework of the so
called crystal basis model of the genetic code. The description allows to
define a not trivial distance between two sequences and to perform the Discrete
Fourier Transform on a sequence. Using the definition of distance the sequence
of $\beta$-globin for Homo, Gallus and Opossum are compared. The Discrete
Fourier Transform for some simple examples is computed.
