Empirical spectra of human and zebrafish. Empirical word frequency spectra showing the two types of behavior described in this paper. The x-axis is the abundance of k-mers, and the y-axis describes the frequency of words with that abundance in the relevant genome. (a) Human genome 11-mers (0 ≤ x ≤ 2,000 occurrences), exhibiting multimodal behavior. (b) Zebrafish genome 10-mer distribution (0 ≤ x ≤ 5,500 occurrences), with a unimodal distribution.