The copy/insert process does not always produce a heavy tailed spectrum. Effect of (a) increasing length of initial genome and (b) adding mutation to the copy/insert process. Graphs show the 11-mer spectrum of simulated genomes with (a) length equal to human chromosome 5, generated using a copy/insert process varying initial genome length, and (b) length 4 Mb, with a proportion of the bases mutated after each insert from an initial genome of 5,000 bp. As both axes are on a logarithmic scale, a distribution with a heavy 'power-law' tail (for example, no mutation) will tend to be a straight line, whereas lighter 'exponential' tails will bend downwards (for example, Bernoulli sequence). The sequences were constructed from an initial genome generated from a Bernoulli sequence with a CG content of 38.5%, matching human chromosome 5, by copying 33 base long chunks.