In spite of normal AMG and PMG invagination, neither anterior nor posterior midgut primordia shows any sign of extension towards each other, but remain as large mesenchymal cell masses immersed in yolk at the ends of the embryo. The cells of these primordia fail to arrange into an epithelium.
Ventral furrow fails to form.
Embryos are partially dorsalised.
sna6/Tp(2;1)Scorv23 adult escapers are occasionally produced, which often have missing halteres or show a hemithorax phenotype. Homozygous embryos fail to form a ventral furrow. Cephalic furrow formation, invagination of the endoderm and germ band elongation do take place in these embryos. Embryos show varying defects in the segmental denticle belts.