Distribution of TEs along the D. melanogaster Release 4 chromosome arms. Numbers of TEs per 50 Kb window are plotted as a function of position along a chromosome arm. Abundance for all families excluding the INE-1 is shown in black for the main and inset panels, and in blue for the INE-1 family in inset panels. Positions of the cytologically estimated boundaries between euchromatin and heterochromatin in pericentromeric regions are shown as red triangles. Positions of genetically estimated boundaries between high and reduced recombination, and between reduced and null recombination, in pericentromeric regions are shown as green and orange triangles respectively. Filled circles indicate centromeric regions that are currently not included in the Release 4 genome sequence. HDRs on the major chromosome arms are numbered in purple.