Breakpoint in Ubx.
A1 tergite is slightly reduced in hemizygote but not in homozygote and ventral pits are formed on A1 to A7, inclusive, in the hemizygote and on A1 in the homozygote. These weak alleles when homozygous survive to adults and appear wild type.
The ventral histoblast nest of A1 is shifted to a more ventral position in flies hemizygous for Ubxbxd-266.
Hemizygotes display thoracic pits on first abdominal segment and first abdominal tergite is slightly shortened laterally.
The phenotype of a number of combinations of Ubx mutations has been investigated to determine the role of the bxd regulatory region in the modulation of Ubx expression.