The loxP cassette in HΔM1-2.w+ has been excised. The locus encodes H lacking introns and carrying carrying a mutation in the first and second possible start codons (amino acid replacements M1V and M18V). As a consequence only the p120 protein isoform can be produced. A residual attR site is present in the 5'UTR and a single loxP site is present in the 3'UTR.
Adult HΔM1-2 homozygous mutants display mild bristle defects with, on average, 2 (out of 40 present in wild-type) of the large head and thorax bristles affected; no abnormalities in wing venation are observed, but the wing size is significantly reduced compared to controls. However, when combined with the HattP allele, the transheterozygotes show very severe bristle defects (around 30 affected).
HΔM1-2/H[+] is a suppressor of visible | adult stage phenotype of DeltaB2
The wing notching phenotype of Df(1)N-54l9/+ heterozygotes is largely suppressed if they are also heterozygous for HΔM1-2.
The vein thickening and vein deltas characteristic for HattP/+ adults is partially suppressible by combination with a single copy of HΔM1-2.