FISH. (A) and (B) illustrate the mapping of the P1 clone P122F9 in cells from the patient no. 3 and in cells from a normal individual, respectively. The P122F9 probe hybridized to both of the der(16) and the der(21) chromosomes, as well as to normal chromosome 16 in patient no. 3. The normal 16 and the der(16) chromosomes are indicated by an arrowhead, and the der(21) chromosome is indicated by an arrow.