Figure 1. A biotinylated satellite (tandem-repeat) probe specific for the heterochromatic region of human chromosome 9 hybridized to normal human lymphocyte metaphase spread. This individual has a much larger block of heterochromatin on one chromosome 9 homologue than on the other. Detection is by avidin–FITC with one round of amplification.

Figure 2. A biotinylated probe prepared by a human-specific polymerase chain reaction (inter-Alu-PCR) from a human–rodent hybrid. The probe has been hybridized to a human metaphase spread prepared from an individual with a translocation between chromosome 9 and chromosome 22. This is an example of ‘reverse chromosome painting’ and shows that the original hybrid contained the long arm of chromosome 9 as its only human material. Detection as in Figure 1.

Figure 3. This is a biotinylated cosmid probe hybridized to a metaphase spread from the same cell line used in Figure 2. Hybridization is to the normal 9 and to the abnormal chromosome 22, showing that the cosmid derives from chromosome 9 distal to the position of the breakpoint in the translocation. Detection as in Figure 1.