  Collapse of the polymer chain upon the sharp decrease of solvent quality is
studied. During collapse, any pair of polymer units appearing in a sufficiently
close vicinity in space has the possibility with a certain probability to form
an irreversible crosslink, thereby preventing the interpenetration of chain
material between the forming clusters. Globular structures having different
spatial chain packing at various scales are obtained by computer simulations.
It is shown that the dependence of probability of contact between two monomers
in space , where s is a distance between monomers along chain, reproduces a
number of characteristic features observed previously in experiments on the
analysis of three-dimensional chromatin packing. The cluster analysis of
intramolecular contact maps makes it possible to express the hypothesis that
there are characteristic discrete hierarchical levels in polymer packing
associated with the number-theoretic origin of rare-event statistics and
inherent to individual maps of intra- and interchromosomal contacts.
