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 18
oC 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 or
sisA, both early acting positive regulators of
Sxl. Fully complements "Sxl
fPR" class (partial deletions of
Sxl information that impair later functions of the gene more than earlier).