  DNA segments and sequences have been studied thoroughly during the past
decades. One of the main problems in computational biology is the
identification of exon-intron structures inside genes using mathematical
techniques. Previous studies have used different methods, such as Fourier
analysis and hidden-Markov models, in order to be able to predict which parts
of a gene correspond to a protein encoding area. In this paper, a semi-Markov
model is applied to 3-base periodic sequences, which characterize the
protein-coding regions of the gene. Analytic forms of the related probabilities
and the corresponding indexes are provided, which yield a description of the
underlying periodic pattern. Last, the previous theoretical results are
illustrated with DNA sequences of synthetic and real data.
