Developmental analysis of some mutants of the bithorax system ofDrosophila.

Mutants in the bithorax system ofDrosophila produce homeotic transformations that affect the mesothoracic, metathoracic and first abdominal segments. In the present report we describe a clonal analysis of the development of those mutants transforming the metathorax and first abdominal segments into mesothorax.The main results indicate that (1) The normal dorsal metathoracic (haltere) disk has similar developmental parameters to the dorsal mesothoracic disk. The main difference is that the initial and final numbers of cells are different in both disks. (2) In flies mutant forBithorax andpostbithorax (which transform the haltere into wing) the transformed haltere disk has the same initial and final number of cells as the normal wing disk. (3) In morphogenetic mosaics homozygousbithorax (andpostbithorax) clones express their genotype autonomously regardless of the genotype of surrounding haltere cells. This autonomy is expressed in a regulation of the number of adult cells per compartment, typical cell affinities and final cuticular differentiation.