Statistical analysis of several properties of the TATA, TATA-1, TATA-2 and TATA-less gene sets. A. The median, 25% and 75% quartile number of exons. B. The median, 25% and 75% quartile length of a single intron. C. The fraction of intron-less genes in the different gene sets. The number of genes in each set is as in Fig. 1. D. The p-values of the differences in the median values (A-C) and intron-less probability (D) were calculated using the Kruskal-Wallis test with Bonferroni correction and chi-square distribution respectively. NS is a non-significant difference (p > 0.05).