Fig. 2. mask tissue is reduced in size. (A) Wild-type (w) third instar eye imaginal disc stained with -BP104, a membrane marker for differentiating photoreceptors (Hortsch et al., 1990). (B) w; mask^6.3/mask^7.29 third instar eye imaginal disc stained with -BP104. (C) Loss-of-function mask clones lacking GFP were much smaller than the wild-type twin spots containing two copies of the GFP transgene. (D) For 21 clones examined, the size of the mutant clone was on average 20.8% the size of the twin spot.