FISH analysis of the leukemic metaphase chromosomes. Chromosome 22 and a phage clone λhp300-2 were detected with TRITC and FITC, respectively. Split signals of λhp300-2 are observed on the boundary between WCP22-painted and unpainted regions of der(11)t(11; 22) and der(22)t(11; 22) (arrows). The intact signal of λhp300-2 was observed on the normal chromosome 22 (arrowhead).