**5. Conclusion**

In This chapter, we investigate the contribution of each coding technique: the linear, the two-dimensional and the structural one in the enhancement of the peaks related to the C. elegans genome periodicities. For this purpose, we use a mean values of smoothed Discrete Fourier Transform applied on sliding window along the DNA sequence to follow the peak evolution for specific frequency points around the frequencies. We detect periodicities around 3, 6, 9 and 10 and found periodicities 3 and 10 related respectively to genes and the positions of the nucleosomes. First we evaluate the frequencies spread through the chromosomes with a 1-D spectrum. Second, we consider the 2-D and 3-D DNA spectrograms to visually detect the specific parts of chromosomes related with protein coding regions, nucleosomes positioning regions, and other particular regions.

The time frequency analysis made it possible to follow the periodicities' evolution. We studied the contribution of a range of binary indicators for the raising of exons' peak frequency. We also studied the localization of the areas being able to form nucleosomes. Thanks to the spectrogram with two dimensions, we visualized the localization of the areas corresponding to periodicity 10 in the limits and not in the center of the helix. The threedimensional spectrogram showed that the raised peaks do not correspond to the periodicity 10 but we see clearly in certain sequences and for some indicators two lines of peaks of variable powers around this periodicity. This result can explain the variation between 10 and 10.7 of the periodicities associated with the nucleosomes presented in the literature. It is also observable that these peaks are alternated around two periodicities; this result could be associated with the phenomena of chromatin compaction.
