Homozygous males show appreciable survival to larval stages (day 5) in the presence of infection with the "male-killing" bacterium S.poulsonii when their mother is also homozygous, while infected heterozygous sibling males show no survival to day 5. Homozygous and heterozygous infected male embryos derived from heterozygous females show no survival to day 5.

In XX cells of Sxl^f1/Sxl^fhv1 females that have adopted the male fate and express a mutant msl-1 protein msl-2 only localises to sites where the mutant msl-1 is bound.

mle binding to X chromosomes of Sxl^f1/Sxl^fhv1 females is dependent on msl-1 and msl-2 function. Sxl^f1/Sxl^fhv1 females that are also homozygous for mutants at msl-1, msl-2 or msl-3 develop as intersexes of the mosaic type.

Less severe allele than msl-1¹.