Fig. 8. Variations in bab derepression in Hth null antennae are correlated with variations in the resulting numbers of tarsal joints. Large hth null clones in the antenna were generated using a Minute (M) mutation on the hth+ chromosome. The hth+ M–/hth+ M– twinspots die, while the hth+ M–/hth– M+ heterozygous tissue surrounding the hth null clones grows poorly. Thus much of the antennal disc comprises hth– M+ tissue and is transformed toward leg. Under these conditions, Bab (purple) is often derepressed uniformly (A), and sometimes derepressed in a modulated pattern (C) resembling that found in the leg. (B) A partially transformed antenna with two joints (arrowheads). (D) A more completely transformed antenna with five tarsal segments and four tarsal joints (arrowheads). The relative frequencies at which these cuticular phenotypes arise suggest that the cuticle in B may derive from a disc with Bab expression similar to that found in A, while the cuticle in D may derive from a disc with Bab expression similar to that found in C. See text for details.
