title: Phenocopies ofBithorax mutants : Genetic and developmental analyses.
abstract: Exposure to ether of wild-type embryos of different strains ofDrosophila melanogaster causes phenocopies of different alleles of thebithorax system. Clonal analysis of the phenocopy spots has shown that the transformation caused by the treatment is maintained by cell heredity. Embryos heterozygous for several recessive mutant alleles ofbithorax show the same frequency of phenocopies as wild-type homozygous sib controls. The same holds for embryos heterozygous for the dominant mutant allelesCbx andUbx1which are point mutants in thecis-regulatory region of the system. However, for dominant mutants which have breakpoints in this region (Ubx80,Ubx130andHm) the frequency of phenocopies is about twice that of their sib controls. Embryos with increasing numbers of copies (from 1 to 4) of thebithorax system show a decreasing frequency of phenocopies. A model is proposed that explains "bithorax" phenocopies as resulting from disturbances in the distribution of positional information signals for segments (inductor molecules) which compete with the product of a regulator gene (repressor) and thecis-regulatory region of thebithorax system. On this model, the initiation of a metathoracic developmental pathway would result from the derepression of thebithorax system.
authors.affiliation: Centro de Biologia Molecular CSIC, Facultad de Ciencias, UAM, Madrid-34, Spain.
authors.forename: M P
authors.initials: MP
authors.lastname: Capdevila
authors.affiliation: Centro de Biologia Molecular CSIC, Facultad de Ciencias, UAM, Madrid-34, Spain.
authors.forename: A
authors.initials: A
authors.lastname: García-Bellido
keywords: Clonal analysis; Determination; Gene regulation; Homoeotic mutants; Phenocopies