MDV integration site preference: Distribution across chicken chromosomes. To determine if MDV preferentially integrated into a specific set of host chromosomes, integration sites for 15 tumors were mapped and analyzed. Chromosomes 4, 6, 12, and 20 are noteworthy as they are shared integration sites among three or more birds. Each tumor is represented by a different color and symbol, which correspond to the tumors depicted in Figure 6 for each bird mapped. Symbols are located to the left of the chromosome for which integration was mapped. If multiple tumors from one bird all share identical integration sites (e.g. Bird 13) then only one set of symbols (e.g. green circles) represents the single transformation event that occurred. If multiple tumors from one bird each have different integration profiles (e.g. Bird 3) then multiple shapes and/or colors (e.g. light blue circles, squares, and triangles) were used. Finally, if a derived cell population was present within a tumor (e.g. Bird 1, T2 and T3) then the sites representing the derived population are depicted as circles outlined in the main tumor color and filled in with a different color (e.g. on GGA 9, 1-T2 and 1-T3).