The NDC1 locus is haploinsufficient. (A) Diploid yeast strains that were either NDC1/NDC1 (HC14–10c/5d; see Table 1), NDC1/ndc1–1 [HC14–10c/HC5–8c(799)], NDC1/ndc1Δ [HC7–31c(1134)/HC14–5d], or ndc1–1/ndc1Δ [HC7–31c(1134)/HC5–8c] were streaked to 5-FOA-containing plates to test whether they are able to lose a plasmid-borne copy of NDC1 (pURA3-ADE3-NDC1; pALR10-NDC1) at 30°C. Asterisks indicate strains that initially contained the plasmid-borne copy of NDC1. (B) A NDC1/ndc1Δ yeast strain [HC14–10c/5d(1197); see Table 1] containing pALR10-NDC1 (pURA3-ADE3-NDC1) was transformed with either a LEU2 vector (pLEU2; pRS425) or with the LEU2 vector containing NDC1 (pLEU2-NDC1; pRS425-NDC1), and the resulting strains were used in a plasmid-sectoring assay. Solid, red colonies indicate a requirement for the plasmid-borne copy of NDC1, whereas sectoring colonies indicate that the cells can lose the NDC1-containing plasmid.