Statistical correlation of nucleotides in a DNA sequence

We review methods in the study of nucleotide correlation in DNA sequence, and demonstrate two basic properties of the correlation through statistical analysis, namely, the short-range dominance of nucleotide correlation in most DNA sequences and the coarse-grained evolutionary dependence of the short-range correlation in coding sequences. A corresponding evolutionary mechanism is suggested. By the use of spectral analysis a large inhomogeneity in long-range base correlations for different sequences is indicated. Some results on three-dimensional DNA walks are reported. The linguistic differences between coding and noncoding sequences are also indicated.