Molecular Genetics of Sexuality in Chlamydomonas

Recent molecular and cellular data on the sexual cycle of Chlamydomonas reinhardtii, a unicellular green alga, is considered in the context of current theories on the origins and evolution of eukaryotic sex. The mating-type locus of C. reinhardtii controls gamete recognition and fusion, organelle inheritance, and sporulation, the three traits that characterize most sexual cycles in lower eukaryotes. The mating-type locus comprises approximately one megabase of DNA on linkage group VI, is highly rearranged in its central region, and contains identified genes that govern both recognition/fusion and chloroplast inheritance. Sporulation, a diploid program designed to negotiate changing environments, is analogous if not homologous to the somatic differentiation program of multicellular plants and animals, and its expression requires the fusion of compatible gametes.