We also investigated the size relevance of introns according to two simple size intervals: ≤1000 bp and >1000 bp. Obviously, the absolute majority of introns in N are small, ≤1000 bp, as opposed to the fact that the greater majority of introns in TS and T are larger, >1000 bp. When examining the median length, we found that intron length increase is correlated with the complexity of RS insertions: TS > T > S > N (Fig. 4). We also observed that the TS intron group tends to be near the 5′-end of genes as opposed to the N intron group that tends to be near the 3′-end of the genes in primates, large mammals, rodents, opossum, and frog, as well as that the TS intron group tends to be near the 5′-end of the genes in platypus, chicken, and anole (Fig. 5). The extremely biased distributions are seen in mouse, where the transposon-rich introns tend to be near the 3′-end, and in zebrafish, where all four intron groups show no significant bias.