Minute mosaics caused by early chromosome loss.

Two genetic operations have been combined in order to ascertain whether there are differential proliferation rates in the syncytial nuclei and the blastoderm cells prior to the formation of the imaginal disc anlagen. Early chromosome loss caused by the mutantca nd has been associated with the generation ofMinute (M/M +) genotypes in normal (M +/M +) zygotes or of non-Minute genotypes inMinute zygotes. The results indicate that there is no growth competition betweenMinute and non-Minute cells prior to the formation of the imaginal discs. Growth competition, however, leads later, during the proliferation phase of the discs, to the demarcation of compartment boundaries within imaginal discs.