Euplotes evolved multiple mating systems which have for long been assumed to be determined by "open" series
of alleles at a single mat locus. Families of mating type-specific pheromones and of their mat coding genes have
been extensively characterized from Euplotes species lying in different positions of Euplotes phylogenetic tree,
and this characterization permitted the study of Euplotes mating systems to evolve from a Mendelian to a
molecular approach. While early branching species (e.g. E. raikovi) show a mating-type determination at a single
mat locus in accord with Mendelian genetics, late branching species (e.g. E. crassus) revealed, in disagreement
with Mendelian genetics, a mating-type determination at two distinct mat loci implying an event of mat-gene
locus duplication. One locus (orthologous) appears to be multi-allelic and deputed to synthesize pheromones
distinctive of different mating types, and the second one (paralogous) deputed to synthesize pheromones that
are structurally identical among different mating types
