Variation in spacer length frequencies across species. (A) A comparison of ACGT elements separated by increasing spacer distance (<31) between two dicots – Arabidopsis and Soybean. Possible common peaks include 0, 14 and 26. Spacer lengths 6–11 show a high degree of correlation between the two genomes. (B) A similar comparison between two monocots – Rice and Sorghum, with possible peaks at 0, 2, 4 and 26. Spacer lengths 0–6 and 18–26 show significant correlation. (C) A 10–90% box and whiskers plot suggests 0 as the only common peak across all species. Interestingly, spacer distance 6 emerges as a common dip in dicots, whereas 12 exists as a common dip in monocots. Arrow – potential common peaks. *** p < 0.001.