FISH analysis of ETV6 and TRKC gene rearranged in the metaphase chromosomes. (A) Split signals of cosmid 163E7 (red) are observed on der(12)(q15) and on der(15)(q25). Large arrow indicates der(12), which is identified by chromosome 12 centromeric probe (D12Z3; green). The small arrows indicate der(15). Note that two der(15)s are detected in most metaphases. Large arrowhead indicates normal chromosome 12. (B) 170I1 BAC probe hybridized with 964c10 YAC probe. The 170I1 BAC (red) that encompasses the breakpoint of TRKC shows split signals on der(15)(q25) and on der(12)(p13). 964c10 YAC (green) covering ETV6 locus splits between der(12)(q15) and der(15)(q25), which results in fusion with 170I1 BAC signal on der(15)(q25). Normal chromosome 15 is indicated by a small arrowhead.