Fecundity of homozygous females reduced, although partial rescue effected by fertilization with sperm carrying mus204⁺. Small but significant increase in X- and fourth-chromosome nondisjunction in the first but not the second meiotic division; X-chromosome recombination reduced to 80% normal levels.

Larval survival hypersensitive to exposure to methyl methanesulfonate, formaldehyde, and ultraviolet light, weakly sensitive to nitrogen mustard, but insensitive to X rays. Hypermutability to alkylating agents; defective both in alkylation and UV excision repair pathways.

Homozygous larvae are sensitive to UV light, formaldehyde and methyl methanesulfonate, but not to X rays or nitrogen mustard. Homozygous females have reduced reproductive capacity, which can be partially rescued when homozygous oocytes are fertilised by wild-type sperm. There is a small but significant increase in X and 4th chromosome non-disjunction.