This method is useful to identify rare heterozygous diploid spore colonies that could be confused with recombinants (Subheading 3.3.4). It is also useful for screening colonies from heterothallic strains to identify homothallic variants, or vice versa, and for screening homothallic colonies for mutants that produce few viable spores, as expected for mutants that make DSBs but do not repair them (“late” Rec mutants).