Studies on transvection at the bithorax complex in Drosophila melanogaster

Summary We have studied the influence of some mutations in the bithorax complex on the observed synapsis dependent phenotype of the genotypes Cbx¹Ubx¹/+ and bx^34e/Ubx¹. The effect of these mutations is similar to that introduced by disruption of pairing or by the z^a mutation. Among the bx mutations, we find that bx⁸ behaves differently from most other bx mutations in its influence on the synapsis dependent phenotype. This observation induced us to map the position of bx⁸ with respect to other bx mutations; we find that it maps between bx^34e and bx³. We show how some of the observations reported here can be fitted into a model of activation of the bithorax complex proposed by one of us.