One-step gene disruption constructs for disruption of HIS3, LEU2, TRP1 or URA3 with each of the other three markers have been constructed. All of these constructs have been tested and found to effectively convert markers either in gene disruptions or on plasmids. The 'swapped' strains allow the unambiguous genetic analysis of synthetic phenotypes with multiple genes, even if the original gene disruptions were made with the same marker. They also allow introduction of multiple plasmids in a single transformant, even if the original plasmids had the same marker, and allow transformation of plasmids into strains containing gene disruptions made with the same marker that is on the plasmids. These 'marker-swap' plasmids therefore eliminate the need for much subcloning to change markers. Marker-swapped alleles are acceptably stable mitotically and meiotically for most applications.