St. 17 gonads immunostained with anti-VASA (germ cells, red) and anti-SOX100B (green). Anterior is to the left in each panel. (A,B) SOX100B-positive PC precursors are observed in both XX (A) and XY (B) tra mutant embryos. (C,D) PC precursors are not observed in either XX (C) or XY (D) gonads when the female form of tra is ectopically expressed using UAS-traF; tubulin-GAL4. (E,F) PC precursors are observed in both XX (A) and XY (B) dsx mutant embryos. (G,H) Df (H99) mutants defective for apoptosis. Note that PC precursors (arrowheads) are still observed in XY (H) but not XX (G) embryos, similar to wild type. In contrast, msSGPs (arrows) are observed in both XY and XX embryos.