The amount of UDP-HexNAc in zygotic mmy^IK63 stage 9-11 embryos is about 50% that of wild type embryos and continuously drops during further development.

mmy^IK63 embryos do not exhibit defects in dorsal mesoderm specification or tracheal development.

mmy^IK63 larvae show a reduction in cuticle deposition and a complete failure of denticle formation and melanization.

Strong allele. Both mmy^IK63 and mmy^IK63/Df(2L)BSC6 larvae show no visible cuticle, ventral denticles or head skeleton. Debris accumulates in the salivary glands. Chitin is absent in the mmy^IK63 larval cuticle. All three cuticle layers are affected: the procuticle varies in thickness and is devoid of lamellar chitin microfibrils, the overlying epicuticle is irregular, and the outermost envelope is reduced to three instead of five alternating electron-dense sheets. Occasionally the cuticle detaches from the epidermal surface. Epithelial organisation is affected in mmy^IK63 mutants. The lateral membrane of epidermal cells is not undulated like in wild type. The ladder-like structures produced by the septate junctions seen in wild type cells are not present in mmy^IK63 epidermal cells, but electron-dense intercellular material is present at the positions usually occupied by the septate junctions. Spacing between the epidermal cells at the adherens junctions is wider in mmy^IK63 larvae than in wild type. Within the tracheal system of mmy^IK63 embryos, some of the narrower ganglionic and dorsal branches are discontinuous. In stage 15 mmy^IK63 mutants, the dorsal trunk fusion branches fail to expand; at stage 16, dorsal trunks develop severe constrictions and dilations in comparison to wild type. The luminal tracheal and apical chitin matrix is absent in mmy^IK63 embryos. However, apicobasal polarity appears normal.