Preferential target sites of piggyBac and Tol2 transposons in HEK 293. A. The genome context of Tol2 and piggyBac target sites. *: both transposons tend to insert near CpG islands more often than expected by chance (Tol2, P < 10-9, piggyBac, P < 10-11; see Methods). B. The gene density around Tol2 and piggyBac target sites. C. Distributions of piggyBac and Tol2 target sequences in various types of repeats. Every bar represents the percentage of target sites found in the type of repeats indicated. The bottom part of each bar represents the percentage of targets located within at least 100 bp to the 3' end of the repeats targeted.