Genetic analysis of mating locus linked mutations in Chlamydomonas reinhardii

The mating-type (mt) locus of Chlamydomonas reinhardii has been analyzed using four mutant strains (imp-1, imp-10, imp-11 and imp-12). All have been shown, or are shown here, to carry mutations linked to either the plus (mt⁺) or the minus (mt^-) locus, and their behavior in complementation tests has allowed us to define several distinct functions for each locus. Specifically, we propose that the mt⁺ locus contains the following genes or regulatory elements: a locus designated sfu, which is necessary for sexual fusion between gametes; a locus designated upp (uniparental plus), which controls aspects of chloroplast gene inheritance and perhaps also zygote maturation; and a locus designated sad, which functions in sexual adhesion. The mt^- locus also contains a sad locus as well as a gene or regulatory element designated mid, which is necessary for the minus dominance in mt⁺/mt^- diploids.