Universal 1∕f noise, crossovers of scaling exponents, and chromosome-specific patterns of guanine-cytosine content in DNA sequences of the human genome

Spatial fluctuations of guanine and cytosine base content (GC%) are studied by spectral analysis for the complete set of human genomic DNA sequences. We find that (i) 1∕f^α decay is universally observed in the power spectra of all 24 chromosomes, and (ii) the exponent α≈1 extends to about 10⁷ bases, one order of magnitude longer than has previously been observed. We further find that (iii) almost all human chromosomes exhibit a crossover from α₁≈1 (1∕f^α₁) at lower frequency to α₂<1 (1∕f^α₂) at higher frequency, typically occurring at around 30 000–100 000 bases, while (iv) the crossover in this frequency range is virtually absent in human chromosome 22. In addition to the universal 1∕f^α noise in power spectra, we find (v) several lines of evidence for chromosome-specific correlation structures, including a 500 000 base long oscillation in human chromosome 21. The universal 1∕f^α spectrum in the human genome is further substantiated by a resistance to reduction in variance of guanine and cytosine content when the window size is increased.