FISH analysis of the ETV6 and JAK2 rearrangements in the ALL case (A and B) and the ALL case (C and D). Hybridization with cosmid 54D5, which spans the 12p13 breakpoint in the CML case, is shown in (A) and (C). Thick arrows indicate the der(12), thin arrows indicate the der(9), and the arrowhead points to the normal 12. (B and D) Hybridization with a mixture of the PACs containing JAK2 and spanning the 9p24 breakpoint. Thin and thick arrows indicate, respectively, the der(9) and the der(12); the arrowhead shows the der(15)t(9; 15; 12); 9N indicates the normal chromosome 9. In (C) and (D) hybridization of a centromere 12 probe is shown in white.