Effect of disrupting default polarity on gradient sensing and mating. MAT a bud1Δ cells expressing in situ–tagged Ste2-GFP were mixed with an equal number of MATα cells and imaged from cytokinesis to fusion. (A) Pie graph showing the proportion of cells with the indicated number of Ste2-GFP polarity patches at the first time point. n = 50 in two trials. (B) Box scatterplot showing the initial angles of Ste2-GFP polarity patches relative to the cytokinesis site (δ values in Fig. 1 E). n = 130 from the 50 cells quantified in A. Mean angle ± SEM = 89.0° ± 4.8°. (C–E) Representative images of mating MATa bud1Δ cells. The fluorescent images show the localization of Ste2-GFP as the MATa cells orient toward their mating partners. (C) A cell with two initial polarity patches. (D) A cell with three initial polarity patches. (E) A cell with four initial polarity patches that mated with two MATα cells. (F–H) Modeling simulations of bud1∆ cells. Outputs from a modified model in which there are two initial polarity sites on the same side of the cell relative to the gradient source (F); two initial polarity sites on opposite sides of the cell relative to the gradient source (G). (H and I) Modeling simulations of partner choice in WT and bud1∆ cells. (H) Outputs from the standard model challenged by two equal gradients with the DS closer to one source. (I) Outputs from a modified model in which a cell with two initial polarity sites is challenged by two equal gradients. Each polarity site is positioned closer to one of the two gradient sources, duplicating the spatial relationships used in the WT simulation shown in H.