(A) A heterozygous diploid generated by mating a naïve strain to one carrying Spok2 undergoes meiosis and generates four spores. One possible outcome of meiosis is depicted. The spores that inherit Spok2 are alive (pigmented), while the spores that do not inherit the Spok2 gene are destroyed (unpigmented, hazard signs). (B) A heterozygous diploid generated by mating the Psk-1 strain (purple) to the Psk-7 strain (green) undergoes meiosis and generates four spores. Note that the Spok block (black oval) is on different chromosomes in the two isolates. Two possible outcomes are depicted: (left) all four spores survive because they all inherited Spok2 and the block that contains Spok3 and Spok4; (right) two of the four spores do not survive because they did not inherit the Spok block.