Crosses between females carrying homozygous germline clones and wild-type males give viable females. Embryos lacking maternal and zygotic Rbf function show ectopic S phases and increased apoptosis. Defects in the pattern of S phases are not seen until mid-stage 12, when the germband is partially retracted. Ectopic S phase cells are first seen in the dorsal epidermis, extending into the ventral epidermis by stages 13 and 14. Extensive apoptosis is seen in the epidermis at stage 13.