FISH of a human RFC probe with chromosomes from B-lineage ALL blasts. (A) is from a hyperdiploid ALL blast with 4 copies of chromosome 21. The green signal is from the RFC gene probe and the red signal from a chromosome 21q22.3-ter probe. (B) is from a nonhyperdiploid ALL blast with 2 copies of chromosome 21, one of which is involved in a 12;21 translocation. The green signal is from the RFC gene probe and the red signal is from a chromosome 12 probe (Coatasome 12).