Trithorax: A new homoeotic mutation of Drosophila melanogaster causing transformations of abdominal and thoracic imaginal segments

Summary

A new homoeotic mutation, trithorax ¹ (trx ¹), of Drosophila melanogaster is described which causes intersegmental transformations in both the adult thorax and abdomen. Specifically, the metathorax and ventral prothorax are partially transformed to mesothroax, whilst abdominal segments are partially transformed towards the first abdominal segment. Three variables are shown to influence the expressivity of the mutant phenotype: (1) presence of wild type copies of the gene in the female parent; (2) culture temperature during the first four hours of embryogenesis; (3) exposure of embryos to ether vapour at the blastoderm stage. In addition it is shown that phenocopies of the mutant phenotype can be induced by ether treatment of heterozygous trx ¹ embryos with a frequency higher than that of bithorax phenocopies in wild type embryos.

These findings are together taken to imply that the mutated gene functions early during embryogenests, and that a common mechanism underlies the determination of all the thoracic and abdominal segments.