Cohybridization of sex-chromosome specific probes and BCR-ABL fusion probes. (A) BCR-ABL–positive cell male cell. Thin arrows point to the ABL (red) and BCR (green) signals; the thick arrow points to the BCR-ABL fusion. The large signals identify the X (red) and Y (green) chromosomes. (B) BCR-ABL–negative male cell. Thin arrows point to the 2 separate ABL (red) and BCR (green) signals. The large signals identify the X (red) and Y (green) chromosomes. Note that the “conventional” dual-color color FISH probe (without additional red signal on the derivative chromosome 9) was used in these experiments.