Evidence of mutational bias associated with repetitive regions of the Coccidioides genomes. For both the C. immitis and C. posadasii genomes, each 1-kb nonoverlapping window of sequence was categorized into a repeat class. Classification is based on the number of homologous copies (n) of that window identified within the genome: nonrepetitive, low (n < 6), mid (n = 6–20), and high (n > 20). The mean GC percentage, the mean CpG frequency, and the fraction of elements with a CpG frequency less than 0.010 were measured for each repeat class. The results indicate that repeats in Coccidioides tend to exhibit a paucity of CpG dinucleotides compared with nonrepetitive regions.