The graph on the left shows genomic AT content (horizontal axis) versus the genomic fractions of alternating pyrimidine/purine stretches of 10 bp (vertical axis). The graph on the right shows a similar plot, but for the fraction of purine stretches (10 bp). With all outliers removed it can be seen from the left graph that there is low linear correlation between genomic fractions of YR stretches and AT content (R2 = 0.12, p < 0.001), while higher correlation persists between purine stretches and AT content (R2 = 0.28, p < 0.001).
Bohlin et al. BMC Genomics 2009 10:346 doi:10.1186/1471-2164-10-346