Flies carrying one copy of Orc1^hs.PA (without heat shock) show no marked phenotype. Flies carrying two copies of Orc1^hs.PA (without heat shock) have no macroscopic phenotypes and females are fertile and deposit eggs with normal chorions. Chorion gene amplification is normal. Flies carrying three or four copies of Orc1^hs.PA (without heat shock) show a wide variety of defects, including lethality during embryonic, larval and pupal stages, male sterility and female sterility. Disruption of the orderly array of ommatidia and bristles in the eye is seen. Incorporation of BrdU is seen in some cells in the morphogenetic furrow (MF) and posterior region of the eye-antennal disc, in contrast to wild type. The onset and duration of the synchronous S phase of cells emerging from the MF is unaffected, and there is no noticeable effect on the proliferation of the imaginal discs. The pattern of DNA replication is essentially wild type during follicle cell proliferation and endoreduplication. However, on entering stage 10B, each follicle cell begins to synchronously incorporate BrdU throughout its nucleus, rather than in discrete subnuclear foci as in wild-type ovaries. Chorion gene amplification is depressed by 1.7- to 3.5-fold in Orc1^hs.PA egg chambers. The eggs laid by females are flaccid and have thin, fragile chorions with defective dorsal appendages.