Mi{iwhite.SNP} contains a single non-functional copy of the w gene ('iwhite_SNP') plus a Disc\RFPDsRed.3xP3.cUa marker. 'iwhite_SNP' is a truncated form of w (both 5' and 3' sequence are missing) into which two silent SNPs have been introduced (one either side of the naturally occurring SacI site).