Chromosomal deletions are important to experimental
genetic analysis in two fundamental ways. First, deletions
fail to complement loss-of-function mutations in
genes located in the chromosomal region of the deletion.
This noncomplementation is the basis for using
deletions to map mutations to specific chromosomal
regions, to screen for new mutations in closely linked
sets of genes and to assess the allelic strengths of new
mutations. Second, heterozygous deletions can enhance
or suppress mutant phenotypes.