Table 2.

Recombination frequency in the cross between different mating-type strains carrying mutations in the pheromone and its receptor genes

Combination		Frequency of recombinants
Parent A (hygR)	Parent B (natR)
M-type strain (WT)	P-type strain (WT)	5 × 10−1
M-type strain (WT)	M-type strain (WT)	<10−7
P-type strain (WT)	P-type strain (WT)	<10−7
M-type strain (pheromoneless)	P-type strain (WT)	<10−7
P-type strain (receptorless)	M-type strain (WT)	3 × 10−7
M-type strain (pheromoneless)	P-type strain (receptorless)	<10−7

The same numbers of cells of parent A and parent B were mixed and cultured on malt extract medium (MEA) for 3 d. Cell suspensions were serially diluted, and aliquots were spread on YEA plates containing the appropriate drug. Colony numbers were counted after several days of incubation.