A Su(var)3-7R2a8 background kills males expressing msl-1Hsp83.PC-msl-2Hsp83.PK. Homozygous Su(var)3-7R2a8 females crossed with transgenic msl-1Hsp83.PC-msl-2Hsp83.PK males produce only 6% of male adult progeny harbouring the transgenes compared to 48% if the mothers are heterozygous for Su(var)3-7R2a8.
When msl-1Hsp83.PC and msl-2Hsp83.PK are expressed in wild-type animals, short wide X chromosomes are seen. The addition of msl-1Hsp83.PC and msl-2Hsp83.PK to roX1ex6 males reduces their viability. roX1ex6, Df(1)52 males have a very low viability, only up to 6.6% of males survive. This loss of viability is partially rescued by adding msl-1Hsp83.PC and msl-2Hsp83.PK, with up to 45% of males surviving.
Expression of msl-2Hsp83.PK in a Iswi2 background (but not in a wild-type background) results in the X chromosome having a bloated morphology in salivary gland polytene chromosome preparations from female larvae. In approximately 30% of the salivary gland nuclei, the phenotype is so severe that the X chromosome is almost completely dispersed and detaches from the chromocenter.
Addition of msl-2Hsp83.PK leads to partial suppression of the abdominal etching phenotype seen in SxlM12/Y males. For SxlM12/Y males with msl-2Hsp83.PK, 72% of their fifth and sixth hemitergites were completely feminized. In contrast none of their forelegs were fully female and 77% were entirely male. The addition of msl-2Hsp83.PK to SxlMf1/Y flies leads to males with completely female genitalia and forelegs, yet nearly normal abdomens.
Females carrying both msl-1Hsp83.PC and msl-2Hsp83.PK do not survive, dying during late larval development. Males carrying both msl-1Hsp83.PC and msl-2Hsp83.PK are fully viable. 72% of msl-1γ269/+ females carrying msl-1Hsp83.PC are viable. msl-1γ269/+ females carrying both msl-1Hsp83.PC and msl-2Hsp83.PK survive to the third larval instar stage. The developmental delay of females carrying msl-2Hsp83.PK is further increased if they are also carrying msl-1MPU or msl-1+tT3UTR, but is unaffected if they are also carrying msl-1+tFL. msl-1γ269/+ females carrying msl-2Hsp83.PK and either msl-1+tFL, msl-1MPU or msl-1+tT3UTR often have a scalloped wing phenotype.