The anterior tergite and intersegmental membrane (ISM) are deleted in heterozygotes and hemizygotes, and replaced with a mirror-image duplication of the posterior tergite and posterior hairy zone (PHZ). Ectopic macrochaetae are often present at the anterior edge of the duplicated tergite structures, and sometimes also in the central tergite. Lines of polarity reversal are not fixed precisely with respect to cuticular pattern. In the most extreme phenotype, polarity is reversed in the middle of the tergite and in the middle of the PHZ. More frequently, the line of polarity reversal is shifted anteriorly in the tergite and posteriorly in the PHZ. The phenotype is stronger in hemizygous males than heterozygous females, and is stronger in more posterior segments. The intertergal region is often compressed, and the dorsal longitudinal muscles show irregular spacing and attachment sites. Ventrally, trichome polarity at the extreme anterior end of the sternite and in the neighbouring pleura is disturbed, but sternal bristles are normal.