  Motivated by the problem of domain formation in chromosomes, we studied a
co--polymer model where only a subset of the monomers feel attractive
interactions. These monomers are displaced randomly from a regularly-spaced
pattern, thus introducing some quenched disorder in the system. Previous work
has shown that in the case of regularly-spaced interacting monomers this chain
can fold into structures characterized by multiple distinct domains of
consecutive segments. In each domain, attractive interactions are balanced by
the entropy cost of forming loops. We show by advanced replica-exchange
simulations that adding disorder in the position of the interacting monomers
further stabilizes these domains. The model suggests that the partitioning of
the chain into well-defined domains of consecutive monomers is a spontaneous
property of heteropolymers. In the case of chromosomes, evolution could have
acted on the spacing of interacting monomers to modulate in a simple way the
underlying domains for functional reasons.
