Locations of chromosomal sequences matching HIV-1 integration site clones are shown as ''lollipops'' above the linear chromosomes. Purple indicates HIV-1; red, HIV-based vector; and green, PIC (in vitro control). The human chromosomes are shown numbered. For each chromosome, the color of the dashes on the upper bar indicates integration within genes (gold) or outside genes (gray). The lower bar indicates relative gene density, with more-gene-dense regions shown as a more intense red. Centromeres are shown by the gray rectangles.