Imprecise excision of the progenitor insertion, resulting in a 1120bp deletion downstream of the original insertion site. This removes part of the dicistronic "lemming" locus, removing all of the upstream open reading frame (lmgA) and the 5' part of the downstream open reading frame (lmgB).

Homozygotes die at prepupal stage P4(i). The mitotic index in third larval instar brains is increased compared to wild type and 50.7 +/- 7.9 % of the cells are polyploid. Third larval instar brains and wing imaginal discs show increased levels of apoptosis compared to wild type. The brain and optic lobes are reduced in size compared to wild type.