Expression of evehs.PS using heat shock from 2.25-2.75 hours after egg laying results in a pair rule phenotype. The segments that remain are about 1.4 times wider than wild-type segments and the cuticle is about 70% the length of a wild-type cuticle. The number of embryos that hatch and the number of adults eclosing is dramatically reduced compared to controls. Parasegments 3 to 6 are unevenly spaced at stage 6-7 with parasegments 3 and 5 being about 1.4 times wider than wild-type and parasegments 4 and 6 being about 0.6 times the wild-type width. The wider parasegments contain about twice the number of cells of the narrower parasegments. The total width and number of cells in all four parasegments is equivalent to wild type. Each of the narrow parasegments maintains a constant relative width until around stage 12. After this time they decrease further in both width and cell number. The wide parasegments remain about 1.3-1.5 times wider and contain about 1.4 times as many cells as a normal parasegment.
Heat shock during the end of cycle 14 causes a reduction of germ band extension similar to that caused by eve mutations. Earlier heat shocks produce even greater reductions in germ band extension.