Polycomb group (Pc-G) genes are needed to maintain expression patterns of the homeotic selector genes of the Antennapedia (Antp-C) and Bithorax (Bx-C) complexes, and hence for the maintenance of segmental determination. Can act as a modifier of position effect variegation (PEV) (By similarity). During S-phase in early embryogenesis. Belongs to the cramped family.