  Partial duality generalizes the fundamental concept of the geometric dual of
an embedded graph. A partial dual is obtained by forming the geometric dual
with respect to only a subset of edges. While geometric duality preserves the
genus of an embedded graph, partial duality does not. Here we are interested in
the problem of determining which edge sets of an embedded graph give rise to a
partial dual of a given genus. This problem turns out to be intimately
connected to the separability of the embedded graph. We determine how
separability is related to the genus of a partial dual. We use this to
characterize partial duals of graphs embedded in the plane, and in the real
projective plane, in terms of a particular type of separation of an embedded
graph. These characterizations are then used to determine a local move relating
all partially dual graphs in the plane and in the real projective plane.
