A quantitative test of long-range correlations and compositional fluctuations in DNA sequences.

Recent findings concerning long-range correlations and fractals in intron-containing DNA sequences of living organisms are tested qualitatively and quantitatively. Extending previous studies, we demonstrate that these findings are trivially equivalent to variations of the base-pair composition in different regions of a DNA sequence. It is shown explicitly that a well-defined scaling or fractal exponent does not exist anywhere. Comparisons of natural DNAs with computer-generated, artificial sequences are made. The present study reveals that certain natural DNA sequences (especially those with compact genomes) do have stochastic characteristics which are intrinsically different from artificial sequences. The results for 21 DNA sequences of various types from widely different taxa are reported.