Mate choice among yeast gametes can purge deleterious mutations

Meiosis in Saccharomyces yeast produces four haploid gametes that usually fuse with each other, an extreme form of self‐fertilization among the products of a single meiosis known as automixis. The gametes signal to each other with sex pheromone. Better‐quality gametes produce stronger signals and are preferred as mates. We suggest that the function of this signalling system is to enable mate choice among the four gametes from a single meiosis and so to promote the clearance of deleterious mutations. To support this claim, we construct a mathematical model that shows that signalling during automixis (i) improves the long‐term fitness of a yeast colony and (ii) lowers its mutational load. We also show that the benefit to signalling is greater with larger numbers of segregating mutations.