Fig. 3. omb in the abdomen. (A) The expression of omb.Gal4, monitored by UAS-lacZ expression. At the front of the ß-gal stripe, the boundary is graded, with staining fading out at about one third of the A compartment. Behind, the stripe ceases about half way into the P compartment. (B) A clone of omb^– cells, marked with singed (yellow arrowheads) which affects the bristles: bristles often become separated from the body of the clone and hence they provide only a poor indication of the extent of the clone. The preparation is stained for ptc.lacZ which is upregulated by Hh (Struhl et al., 1997b) both inside and outside the clone. Note the omb^– territory forms unpigmented (a6) cuticle at the back of the A compartment and lightly pigmented (a3) cuticle more anteriorly, in place of the normal dusky (a4) cuticle (Fig. 2). Polarity in the clone is reversed. (C) A clone of omb^– cells, marked with ß-gal. The clone is associated with a patch of reversed polarity which, here and there, extends both in front and behind the clone (visible in the hairs and indicated by the red arrows pointing upwards). The clone itself lacks the dark a4 pigment which is visible anterior and lateral to the clone. Inset shows detail of hair reversals in front of the clone. (D) A clone of omb^– cells, marked with ß-gal. This clone is near the back of the A compartment and contains largely reversed hairs; note the autonomy of the effects of omb^– on pigment, and the non-autonomy of its effects on polarity. The white arrowhead indicates a patch of dusky (a4) pigment that is just anterior to the clone. Compare Fig. 4B. (E) A clone overexpressing omb, marked with ß-gal. We see the hairs pointing into the centre of the clone giving reversed polarity behind it. In the middle and at the back of the A compartments, clones of this genotype give abnormal cuticle, with reduced pigmentation (not shown). Compare Fig. 4D.