Point mutation.
Mutant chromosome acts as a dosage sensitive maternal modifier of run : causes tergite defects in greater than 40% of run3 heterozygotes. Heterozygous run embryos derived from heterozygous l(2)41Ae34-4, Nipped-A1/+ females show run-associated abdominal segmentation defects. Similar effects are seen with heterozygotes for Kr and eve mutations. Maternal heterozygosity for l(2)41Ae34-4, Nipped-A1 has no effect on the viability of Kr heterozygotes.
Chromosome carrying Nipped-A1 is a double mutant chromosome, and also carries l(2)41Ae34-4.