Figure 6. P-cells preferentially mate with wild-type M-cells.

(A) Experimental design. Wild-type P-cells (P_WT) were mixed with an equal number of wild-type M-cells (M_WT) and M-factor-less M-cells (M_mut), marked by the ade6-M210 auxotrophic marker, in nitrogen-free medium. If the P-cell chose an ade6 ⁺ M-cell, the descendant spore clones would have no ade6-M210 allele. If the P-cell chose an ade6-M210 M-cell, the allele would be transmitted to half of the descendant spore clones. Thus, the preference of P-cells for type of mating partner could be determined by the frequency of ade6-M210 segregants. (B) Experimental results. The following strains were used: L972 (h ^– prototrophic), L975 (h ⁺ prototrophic), FS120 (h ^– mfm1,2,3Δ ade6-M210), and FS121 (h ^– mfm1,2,3 ⁺ ade6-M210). The mixed cells were allowed to mate, and resulting hybrid diploids were sporulated. Spores were isolated by micromanipulation and grown on nutrient medium with adenine sulfate limitation.