10.4% of eggs derived from homozygous female germline clones show a fused dorsal appendage phenotype. Eggs also occasionally show a "curled" phenotype, in which the ends of the dorsal appendages curl around to form a hook-like shape. None of the eggs hatch.

Homozygous follicle cell clones are smaller than wild-type clones both in early, proliferating egg chambers and in late, endocycling egg chambers.

Mutant larvae die at an early stage, developing to the L2 stage, but with a size comparable to L1.

Upf1^26A mutants do not exhibit defects in larval cell differentiation. Larval tracheal cells lacking Upf1 display wild-type morphology at all levels of branching, including tracheal terminal cell clones, which show normal branching patterns and luminal structures. Likewise, type IV da neurons appear normal in these mutants.

While homozygous mutant Upf1^26A clones are readily obtained from the larval tracheal system, clones are not recovered in the adult system. Large clones are also not recovered from the adult epidermis or eyes, Although small peripheral eye clones are occasionally observed.