The purpose of the backcross to the parents is to provide four distinct groups of flies in the F2 generation. One group displays all three mutations and will therefore contain no new mutant chromosome. The homozygous Plumb eye group will die. The Curly Lobed and the Plumb groups will be heterozygous for one of the desired chromosomes in question. If you self either group, you will obtain flies homozygous for the experimental chromosome and if a recessive mutation is contained on that chromosome, the phenotypic condition will be seen. Flip to the next card for the selfing cross with Plumb eyed flies.
