A cDNA fragment containing mutated H sequence has been reintroduced into the attP site present in HattP, resulting in a H locus lacking introns and 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 loxP cassette containing a w[+] marker is present in the 3'UTR.
Adult HΔM1-2.w+ homozygous mutants display rather severe bristle defects with, on average, 20 (out of 40 present in wild-type) of the large head and thorax bristles affected. Wing venation remains largely normal.