Recombination between the FRT sites present in the progenitor insertions (P{RS3}CB-5266-3 and P{RS5}5-SZ-3429), deleting the intervening genomic sequence (predicted to delete from 401bp of the Grip 5'UTR through to 2083bp downstream of the Grip 3'UTR).
GripB-LO1 mutants exhibit abnormal muscle patterning.