Substitution of 2 bases for 3 in a region of exon 5 present in all mRNAs (change from gaattTACatttcca to gaattAAatttcca). This introduces a stop codon before the conserved RNA-binding part of Dvir\Sxl.
Only 0.1% of Dvir\Sxlf1/Dvir\Sxlf3 females survive.