Polytene chromosomes normal.
Point mutation.
Mutations in the m9/m10 coding region.
Homozygotes differentiate clusters of extra chaetae preferentially in the lateral regions of the tergites. This phenotype is exaggerated in heterozygotes with the revertant alleles E(spl)rv1 and Df(3R)E(spl)-rv27.
Clusters of chaetae in the lateral region of the notum and extra microchaetae in the scutellum.
Weak neurogenic phenotype.