Embryonic segmentation is normal. Transheterozygotes with kn¹ enhance the kn¹ wing vein phenotype, the veins are extensively fused. This loss of intervein region reduced the length and width of the wings by 80-90%. The transition point between socketed and unsocketed bristles at the wing margin is shifted posteriorly to the shifted position of wing vein L3. Clones generated in adult cuticle are normal unless induced in the anterior compartment of the wing in the intervein region between veins L3 and L4. Clones obey the A-P compartment boundary but when they are induced along the boundary the result is an ectopic or shifted vein with an associated loss of vein L4 in the non-mutant posterior compartment. Clones located at the wing margin generated terminal vein 3 bristles rather than true marginal bristles. Doubly mutant mosaic clones with ptc^S2 are very similar to clones mutant for ptc^S2 alone that affect global organisation: reorganisation of the wing when induced in the anterior compartment and clones induced near the anterior margin induce a complete duplication of the anterior wing blade. The kn mutant affects local alteration in wing patterning associated with ptc inactivation.