When the yolk protein 1 (YP1) is mutated, ZAM particles are frequently visualized in association with the Golgi apparatus in the follicle cells, and in the superficial layer of the yolk granules in the oocyte. A and B, stage 9 ovarian chambers heterozygous XU/XS and XU/fs(1)1163 respectively, show fewer than normal anti-Gag binding sites in the follicle cells than XU/XU ovarian chambers (see Fig 1A) (Scale Bar, 400 nm). An enlargement of the area defined by the black rectangle is presented below Fig. A and B. ZAM viral particles are preferentially associated with the Golgi apparatus in the follicle cells as presented in C (Scale Bar, 100 nm), or with the yolk granules in the cortical ooplasm as presented in D (Scale Bar, 100 nm). Legend is as in figure 2.