Developmental analysis of the homoeotic mutation bithoraxoid of Drosophila melanogaster.

The homoeotic transformations caused by bxd are described in detail. The anterior histoblast nests of the first abdominal segment are missing, and are replaced by one or two leg discs ventrally. Mainly anterior compartment patterns are found in the ectopic, abdominal legs of adult flies. However, cell lineage analyses show that both anterior and posterior polyclones are established early in the development of these ectopic legs, but the posterior polyclone is smaller. Cells of the anterior polyclone may regulate later in development to adjust for this and form pattern elements normally derived from the posterior polyclone. In addition, experiments show that bxd+ is required by the second larval instar stage, and possibly as early as the blastoderm stage.