Traverse from source GO down children.

def _traverse_relationship_rev_objs(self, rel2dst2srcs, goobj_parent, goids_seen):
        """Traverse from source GO down children."""
        parent_id = goobj_parent.id
        goids_seen.add(parent_id)
        ##A self.go2obj[parent_id] = goobj_parent
        # Update goids_seen and go2obj with parent alt_ids
        for goid_altid in goobj_parent.alt_ids:
            goids_seen.add(goid_altid)
            ##A self.go2obj[goid_altid] = goobj_parent
        # Loop through children
        for reltype, recs in goobj_parent.relationship.items():
            if reltype in self.relationships:
                for relrev_obj in recs:
                    relrev_id = relrev_obj.id
                    rel2dst2srcs[relrev_id].add(parent_id)
                    # If child has not been seen, traverse
                    if relrev_id not in goids_seen:
                        ##F self._traverse_relrev_objs(rel2dst2srcs, relrev_obj, go2obj, goids_seen)
                        self._traverse_relationship_rev_objs(rel2dst2srcs, relrev_obj, goids_seen)