FISH analysis of TEL/AML1-positive cord blood. One negative (A) and 3 TEL/AML1-positive (B-D) cells. All the positive cells show the TEL/AML1 fusion signal (yellow), presence of the nontranslocated TEL allele (green), and 2 red signals demonstrating 1 normal AML1 and 1 signal from the disrupted AML1 allele.