Numerical and structural variants (47,XXX; 92,XXXX; 47,XYY; 92,XXYY; 92,lh+lh+) were used to determine the topography of chromatins of different molecular composition in cultivated fibroblast-like cells. In postlogarithmic populations of interphase nuclei, the statistical patterns of chromocenter distributions of 2n and 4n strains were similar, as were the principal modes of the lh+ and X strains. A different pattern was obtained for the pair of Y bodies, and there were classes with intimate associations of chromocenters in both the Y and lh+ strains. It appears that (1) “ectopic pairing” involves specific chromosomes by virtue of segments of constitutive heterochromatin; (2) certain chromosomes are attracted to nuclear structures such as the nuclear margin (inactive X) or the nucleolus (Y), whereas others are not (lh+); and (3) homeologous genomes tend to remain segregated in euploid nuclei of tetraploid cultures; observations on the behavior of the lh+ homeologs during nuclear division were consistent with this interpretation, but quantitation at mitosis may be difficult with human material.