  Chromatin is known to be organised into multiple domains of varying sizes and
compaction. While these domains are often imagined as static structures, they
are highly dynamic and show cell-to-cell variability. Since processes such as
gene regulation and DNA replication occur in the context of these domains, it
is important to understand their organization, fluctuation and dynamics. To
simulate chromatin domains, one requires knowledge of interaction strengths
among chromatin segments. Here, we derive interaction strength parameters from
experimentally known contact maps, and use it to predict chromatin organization
and dynamics. Taking $\alpha$-globin domain as an example, we investigate its
3D organization, size/shape fluctuations, and dynamics of different segments
within a domain, accounting for hydrodynamic effects. Perturbing the
interaction strengths systematically, we quantify how epigenetic changes can
alter the spatio-temporal nature of the domains. Computing
distance-distributions and relaxation times for different chromatin states, we
show that weak and strong interactions cooperatively determine the organization
of the domains and how the solid-like and liquid-like nature of chromatin gets
altered as we vary epigenetic states. Quantifying dynamics of chromatin
segments within a domain, we show how the competition between polymer entropy
and interaction energy influence the timescales of loop formation and
maintenance of stable loops.
