P{Mcp-w#14} insertion is located 87bp upstream of the first exon of the less extensive of the two splice variants of the AP-2 transcription unit, and thus is within the first intron of the more extensive of the two splice variants of the AP-2 transcription unit.
Homozygotes are viable but have short legs. The joints of the legs are missing. The sex combs and transverse rows are correctly positioned. The first leg is most strongly affected. The second and third legs are slightly longer but also fail to form joints.
Etymology: 'stummelbein' is German for 'short leg'. Reversion analysis indicates that the P{Mcp-w#14} insertion is the cause of the mutant phenotype.