Imprecise excision of the progenitor insertion, resulting in a deletion of RYBP nucleotides 322-853. This removes sequences of the 5' UTR as well as the N-terminal sequences encoding the NZF domain.
Homozygous animals die progressively throughout development and are developmentally delayed. Very infrequently, homozygous adults have a distal gap in the L5 wing vein, an umbrella-shaped wing or malformed mesothoracic legs.