The attP-flanked w+ marker present in atow has been replaced with full-length wild-type ato, using phiC31:int-mediated recombination. The inserted ato sequence is flanked by inverted attR sites generated during the recombination event.
atoato mutant flies are viable and do not show any adult eye morphology defects but the mutant ommatidia almost always contain two pros-positive photoreceptor neurons instead of one.