Flies of the 'abnormal abdomen' strain have a higher level of Dmer\bb units with Dmer\R1-element and Dmer\R2-element insertions than wild-type flies. Uninserted Dmer\bb units do not undergo general underreplication in contrast to wild-type, although differential underreplication of the inserted Dmer\bb units does occur in the 'abnormal abdomen' strain.
Mutants have delayed production of juvenile hormone esterase and juvenilized abdominal cuticle. Egg to adult developmental time is slowed down by 0.92 days in females bearing the Dmer\uraa allele in nature, with no detectable slowdown in males. Females bearing the Dmer\uraa allele have a strong fecundity advantage in nature under some ecological conditions but not others.
Phenotype is only manifest when more than a third of the 18S/28S rDNA repeats are transcriptionally inactivated by the insertion of R1 repeats.