  This paper provides results on the modular representation theory of the
supergroup $GL(m|n).$ Working over a field of arbitrary characteristic, we
prove that the explicit combinatorics of certain crystal graphs describe the
representation theory of a modular analogue of the Bernstein-Gelfand-Gelfand
category $\mathcal{O}$. In particular, we obtain a linkage principle and
describe the effect of certain translation functors on irreducible
supermodules. Furthermore, our approach accounts for the fact that $GL(m|n)$
has non-conjugate Borel subgroups and we show how Serganova's odd reflections
give rise to canonical crystal isomorphisms.
