Fig. 2. The frequency distributions, shown as pie charts, of the ‘typical’ pattern (those shown in Fig. 1) are 15-20 times more frequent than some of the other patterns detected among those expected, on the basis of the combined possibilities of the three categories (condensation, proximity and position) in which we placed the fluorescent signals. Blue represents condensed, overlapping signals, either central or peripheral; dark blue and purple represent condensed, opposite ends, either central or peripheral, depending on the number of hybridization signals; pink, brown and light brown represent decondensed, opposite ends, both central and peripheral, depending on the number of hybridization signals. In the Rb heterozygotes, the spatial relationship between the Rb metacentric chromosome arms and their telocentric homologues differs from that of the homozygotes (yellow).