To find insertions into a specific region on chromosome 3, the researcher separately crosses individual F2 male flies with eye pigment to females heterozygous for a deletion on chromosome 3. Since this deletion is homozygous lethal (as most large deletions are), she uses flies that have one copy of a normal chromosome 3 as well as one copy with the deletion. The normal (non-deleted) chromosome 3 also carries a dominant mutation called Serrate, which produces notched wings. (This non-deleted chromosome also does not allow for recombination with the chromosome with the deletion). The females are also homozygous for the white mutation, meaning that any progeny with eye pigment will have a P-element insertion with its mini white marker. In this way, the researcher hopes to find P-element insertions in her screen that do not survive when paired with the deletion -- indicating that the insertions are in the region spanned by the deletion, and have caused a mutation in a gene essential for survival. When the researcher examines the progeny with eye pigment that result from these crosses, she finds two different categories of flies. Some crosses produce flies with eye pigment and notched wings, as well as flies with eye pigment and normal wings. Other crosses produce flies with eye pigment and notched wings, but no flies with eye pigment and normal wings. What might explain these results