Self-induction of a same-sex white a/a biofilm depends upon the α-pheromone receptor STE2 and the α-pheromone gene MFα, but not the a-pheromone receptor STE3 or the a-pheromone gene MFa. Analysis was performed on 48-h biofilms of the parental strain P37005; the ste2/ste2, mfα/mfα, ste3/ste3, and mfa/mfa deletion mutants; and the ste2/ste2-STE2, mfα/mfα-MFα, ste3/ste3-STE3, and mfa/mfa-MFa complemented mutant strains. (A) Biofilm biomass; (B) safranin O straining of biofilms, a reflection of biomass; (C) biofilm thickness; (D) β-glucan released into the supernatant; (E) cell density of biofilms at the substratum; (F) gene expression, measured by RT-PCR. ACT1 expression serves as a control for equal loading. Bar in panel E, 100 μm.