FISH analyses of inv(16) and

MLL deletions. With the LSI CBFBdual-color probe, the normal 16q22 region appears as adjacent red-green or a fused yellow signal. On a metaphase preparation, the inv(16) will have red and green signals on opposite arms of the aberrant chromosome. (A) Expected signal pattern with the LSI CBFB of a metaphase containing an inv(16), with red and green signals appearing on opposite arms of the inverted 16 chromosome. (B) Atypical signal pattern with LSI CBFB of a metaphase containing inv(16) and deletion of 3′ sequences of CBFB gene. Spectrum Green–labeled probe failed to hybridize to the 16q22 region, providing evidence that at least 170 kb of the region 3′ to CBFB gene is deleted with this inversion. (C) Interphase nucleus and metaphase cell showing the results of LSI MLL hybridized to a specimen possessing a t(11;17)(q23;p13). As expected for a rearrangement at theMLL breakpoint, the orange signal has moved to the p arm of chromosome 19, and the green signal has remained on the q arm of chromosome 11. On the normal chromosome 11 the LSI MLL probe green and orange signals (fused yellow) remain unchanged. The interphase nucleus showed one green/orange fused signal representing the normal chromosome 11 and separate green and orange signals representing the translocation chromosomes. (D) Atypical signal pattern with LSI MLL of a metaphase containing t(9;11)(p22;q23) accompanied by the deletion of a 3′ region of MLL gene with the corresponding loss of orange signal. Spectrum Orange–labeled probe failed to hybridize to the 3′ region of MLL gene, providing the evidence that at least 190 kb of the region that is telomeric to the gene was deleted.