Fig. 4. Cells respond more to the Stan system in the absence of the Ds system. A twofold increase in the dose of the fz gene (between clone and surround) has no effect in wild-type flies (not shown) but, in ds^- flies, reverses polarity in front of the clone and imposes normal polarity behind the clone (A). Only a small effect (yellow arrowhead) is seen in a ds⁺/ds^- fly (B). Clones are marked with trc. Anterior is towards the top, red lines outline the clone and red arrows indicate the polarity imposed on cells outside the clone.