Defective in some very early steps in the sex-determination process, but which has no adverse effect on the growth or sexual development of homozygous mutant diplo-X clones induced by mitotic recombination. Rare escapers at 18o
C are phenotypically female; nevertheless, it has a dominant masculinizing effect on the phenotype of triploid intersexes ( 2X:3A ) and interacts in a dominant-lethal fashion with mutations in da
, both early acting positive regulators of Sxl
. Fully complements "SxlfPR
" class (partial deletions of Sxl
information that impair later functions of the gene more than earlier).